What are Estoppels?
Estoppel refers to a rule of law whereby a party to litigation is stopped from asserting or denying a fact. It is a rule of exclusion which makes evidence improve or disprove of a fact inadmissible. There is said to be an estoppel when one is forbidden in law to speak against his own act or deed even though that person is trying to tell the truth. For that reason then Estoppel amounts to a disability which precludes parties from alleging or proving illegal proceedings that a fact is otherwise than it has been made to appear by the matter giving rise to the disability. Essentially at a conceptual level estoppel will stop a person from bringing in information, which should be at variance with actions that this person has engaged in before.
Estoppel has different aspects. You can look at it from adjectival or procedure. The fact aspect is as a rule of evidence and in this capacity of adjectival procedural realm, it makes evidence inadmissible.
The second aspect which is still a rule of procedure is as a facet of the law of pleadings. The party who proposes to rely on estoppel must raise it in the proceedings. If the person fails to raise estoppel in the pleadings, it can amount to a waiver of the Estoppel.
Moorgate Mercantile Co Ltd v. Twitchings  3 AER 302
This case is authority for the proposition that you must plead your estoppel.
The Plaintiffs a finance company, were members of an organisation, HP Information Ltd (HPI), set up to prevent fraud in connection with hire-purchase agreements. Finance Companies would inform HPI of any hire purchase agreement that they had entered into in relation to a car so that in the event of a car dealer being offered a car for sale, the dealer could contact HPI to discover whether it was the subject of a hire-purchase agreement. The Plaintiff’s let a car on hire-purchase to M. By some unidentified mistake or oversight on the part of the plaintiffs, HPI were not informed of the agreement. M, falsely asserting that he was the owner of the car, offered it for sale to the defendant, a car dealer. The defendant contacted HPI, who informed him that the car was not registered with them. The defendant bought the car and later sold it. The plaintiffs sued the defendant for its conversion. A majority of the House of Lords held that the plaintiffs were under no legal duty to the defendant to register or to take reasonable care in registering with HPI the hire-purchase agreement in question and accordingly that an estoppel by negligence could not arise to prevent them from proving their claim against the defendant.
The third aspect of estoppel is as a facet of substantive law and it can amount to a defence barring the plaintiff from proving some fact essential to his or her case. Our Evidence Act does not define Estoppel and the definitions of Estoppel that we have are drawn from case law and the original source of the word Estoppel which is drawn from French word which means stop!
Law v. Bourveries 3 ch. 82
The case illustrates Estoppel as a rule of evidence and cannot be used to found an action. Can only be used as a shield and not as a sword. It is a substantive right that can bar a plaintiff from bringing in a fact;
Some principles as to estoppel!
1. Estoppel has to be mutual or reciprocal and consequently has to bind both parties; A stranger can neither take advantage of nor be bound by Estoppel.
2. Estoppel cannot be used to circumvent the law so you couldn’t invoke estoppel to render an invalid act valid or vice versa.
3. Estoppels must be certain and this is to say that the statement which forms the basis of an estoppel should be precise clear and unambiguous. It should be incapable of being read in more than one way. It should lead a person to just one conclusion.
4. It is immaterial whether the makeup of the statement or the representor believes it to be true or false i.e. if you make a reckless statement which lead people to make reckless statements to their detriment, you will be estopped.
5. The representation which is the basis of an estoppel must be a statement or representation of fact which existed in the past or is existing at the time of the making of the statement or representation. It should not be a promise in futuro
6. It is not essential that intention to deceive or defraud must be there for estoppel to be there. Suffice it that you made the representation and a person has changed their statement then estoppel will arise.
The effect of estoppel is to bind a party and to prevent them from relying on certain facts and denying certain facts. A good example is the case of Moorgate V. Twitchings where an owner of property entrusted his property to the care of another person. By his conduct that other party had albeit unintentionally by his conduct led a third party to believe the owner had no title to the property. The third party acted in reliance to that belief and the owner was held estopped from asserting his title against that third party who had acted in the belief that the owner had no title because of the representation through conduct of the owner who had been left in charge of property. This person acted on the best evidence that he had. Only the person in charge of the property would have known better. And the court held that the owner was estopped from
CRABB V. ARUN District Council 1976 1 Ch 179
The plaintiff owned a piece of land which had access at point A on to a road owned by the defendants. And the Plaintiff also had a right of way from that point A along this road. To enable him to sell his land in two parts, the plaintiff sought from the defendant a second access point and he also wanted a further right of way from point B. at a site meeting held between the plaintiff, his architect and a representative of the Defendant, the additional point B was agreed to. Subsequently the defendants fenced the boundary between their road and the plaintiff’s land erecting gates at B and A. after the Plaintiff sold part of his land together with the right of access at A and also going with the right of way onto the road, the defendants removed the gates at B and fenced the gaps. Essentially that blocked the links between A and B the Plaintiff sued for a declaration and injunction claiming that the Defendants were estopped by their conduct from denying him a right of access at B and a right of way along the road. The trial court held that in the absence of a definite assurance by the defendant no questions of estoppel could arise. There were no assurances that he would forever have the right of way at B. consequently the plaintiff’s action was dismissed. On Appeal by the plaintiff, it was held that
- The defendants knowing the plaintiff’s intention to sell his land in separate portions by their representations led the Plaintiff to believe that he would be granted a right of access at B and by erecting the gate and failing to disabuse him of his belief encouraged the plaintiff to act to his detriment.
- Equity should be satisfied by granting the plaintiff a right of access at B and a right of way along the road.
- In view of the sterilization of the plaintiff’s land for a considerable period resulting from the Defendant’s acts, the right should be granted without any payment by the Plaintiff.
There are 4 general classifications of Estoppel
1. Estoppel by Record
2. Estoppel by Deed
3. Estoppel by Agreement
4. Estoppel by Conduct.
ESTOPPEL BY RECORD
Arises mostly out of judgments and is predicated on the premise that in the interest of the public there should be an end to litigation. It is important that once a matter is adjudicated upon, parties do not live in fear of its being subsequently resurrected. After a judgment has been announced by a court of competent jurisdiction, the unsuccessful party cannot challenge this judgment by raising the same point in another action against the successful party. The prerequisites for there to be estoppel by record is that the matter should have been adjudicated by a court of competent jurisdiction and a matter adjudicated upon by a court of competent jurisdiction cannot be reopened.
Records refer to both proceedings and judgment and for estoppel to arise the judgment has to be impeachable so estoppel or record arises when an issue of fact has been judiciary determined in a final manner between the parties by a competent court and the same issue comes directly in question in subsequent proceedings between the same parties.
For the purposes of Estoppel by Record judgments are divided into two.
1. Judgments in rem
2. Judgments in personnam
A judgment in rem is an adjudication on the status of a person or a thing and examples of judgments in rem will be judgments in divorce proceedings, probate proceedings, bankruptcy proceedings. All these have implications for the status of persons or things. Section 44 (1) of the Evidence Act defines judgments in rem.
Essentially the judgments are conclusive proof of the matters they adjudicate against all persons in the world. Not as against any specified persons but absolutely. And as between parties to the suit it is conclusive evidence for the reasons for the decision.
Judgments in personam are those that do not fall within the definition in S. 44 i.e. do not affect the status of person or thing e.g. judgments involving contracts or torts. They are conclusive proof as to the matters adjudicated upon and the reasons for the judgment between the parties to the proceedings. They do not bind the whole world but only the parties to the proceedings.
Both judgments in rem and in personam give rise to 2 kinds of estoppels
1. Cause of Action Estoppel
2. Issue Estoppel
Course of action, once an issue has been adjudicated the same persons cannot bring it up again
Course of Action Estoppel is based on the notion that a course of action is dealt with on a judgment and so parties to the action will be prevented from asserting or denying as against what was found so if a particular course of action was found to exist or not to exist, the same parties will not be allowed to revisit the same issue. But note that it should have been the same parties. Parties can be injured by the finality of this course of action.. a good example is the case of
CONQUER V. BOOT  2 KBR 336
In this case the plaintiff had received decision on a course of action arising out of the defendant’s breach of a warranty to build a house in a good and workman like manner. It was held that the plaintiff was estopped from making a claim for further loss (the plaintiff had already been paid damages) by reason of same breach of warranty which he had suffered subsequent to the original litigation.
PURSER V. JACKSON  QB
Where a contract provides for arbitration in respect of disputes as and when they arise an earlier submission to arbitration does not prevent the submission to arbitration of a dispute which subsequently arises. The earlier submission operates as an estoppel only in respect of the matters which it actually covered. If parties agree that they will submit their grievances when they arise the fact that you have given the matter to arbitration. The estoppel operates only as estoppel on matters that were covered in the pleadings so you could still bring other matters.
There are 3 main distinctions
Issue Estoppel applies only to the issues raised and actually determined in the earlier proceedings. It cannot arise where a party has come into possession of fresh evidence.
With regard however to course of action estoppel it can actually apply not just in respect of matters that a court was called to decide upon but also matters which the plaintiff exercising due diligence or reasonable diligence could have brought forward against the defendant. All matters or claims against the defendants which the plaintiff exercising diligent powers could have brought forward. Only these will form the basis of the Estoppel.
Whether it be issue estoppel or course of action estoppel the requirement of estoppel by record are the same apart from the nuances that you go to stay a final judgment, same parties litigating in the same capacity and same issues. When you talk of same parties estoppel only operates when the parties are the same as the parties in the original suit. It does not have to be them in person but it could also be their agents.
TOWNSEND V. BISHOP  1 AER 803
A plaintiff claimed damages for injuries he sustained while driving his father’s car which collided with the defendant’s lorry. In earlier proceedings brought by the father against the defendant, in respect of the damages to the car the defendant had succeeded on a plea of contributory negligence on the part of the son who had been active as his father’s agent. The law at that time was that contributory negligence was a complete defence. On a plea by the defendant or course of action Estoppel it was held that the parties to the 2 actions being different, the plaintiff was not estopped from denying his contributory negligence.
An Estoppel by record can only arise where parties to the proceedings litigate in the same capacity as they did in their previous proceedings.
Marginson v. Balckburn  2 KB 726
There was a collision between Marginson’s car driven by his wife as his agent and an omnibus driven by Blackburn servant. Marginson’s wife died, Marginson was injured and several houses were damaged as a consequence of the accident. Owners of the houses succeeded in an earlier action for damages against Marginson and Blackburn. It was held that both Marginson and Blackburn were vicariously liable for the negligence of their respective drivers who were adjudged equally to blame. Estoppel was alleged and it was held that Marginson was estopped from denying his wife’s contributory negligence in relation to the claim. As her personal representative he was not stopped from denying her contributory negligence because he appeared in a different capacity from that which he had litigated before.
Finally on same issues, Estoppel will only operate if the issue with the proceedings in question is the same in that which was pleaded. The court will refer to the pleadings argued and reasons given for the judgment.
Randolph V. Tuck  1 QB 175
MILLS V. COOPER  2 Q.B. 459
HENDERSON V. HENDERSON [1843 – 1860] AER 310
LIMITATIONS TO ESTOPPEL BY RECORD
1. Matrimonial Cases: Matrimonial causes are not entirely adversarial. Essentially estoppels in a matrimonial cause will bind the parties to the matrimonial cause but not the court.
Thomson v. Thomson:
“Once an issue of a matrimonial offence has been litigated between parties and decided by a competent court, neither party can claim as of right to reopen the issue and litigate it all over again if the other party objects. However the divorce court has the right and indeed the duty in a proper case to reopen the issue or to allow either party to reopen it despite the objection of the other party.”
If the party objects to reopening of the case, one could not open the issue without going to court.
In criminal cases the course of action estoppel will be pleaded by the plea of autre fois acquit (accused was previously acquitted) and autre fois convict (accused was previously convicted).
An accused is estopped from denying his guilt or wrong in a subsequent trial where guilt issue arises. This is provided for in Section 47 (a)
Robinson V. Oluoch
Queens Drycleaners V. East African com et al
In both these cases the court emphasized that in civil and criminal proceedings, the accused is estopped from denying the conclusive nature of his conviction i.e. if an accused is found guilty of dangerous driving, then a subsequent suit if filed for negligent behaviour the accused is estopped from denying.
A judgment in a civil case is not conclusive proof of matters decided in a criminal case. It would be admitted as relevant to the issue but standard proof will be much higher.
ESTOPPEL BY DEED:
The principle underlined here is that persons who make solemn assertions or engagements under seal must be bound by those engagements. Parties to a formally executed and sealed deed and their privies by any evidence which is less formal and solemn.
This Role is subjected to:
1. It only applies between parties of privies to the deed and only in proceedings on the deed.
2. No Estoppel will arise upon recitals or descriptions which are immaterial or not intended to bind (there will be instances where a recital …)
3. No Estoppel arises where deed is tainted with fraud or illegality.
For a recital to a deed to form the basis of estoppel by deed, it has to contain: -
- Unequivocal statement of facts;
- There has been a contract as a result of the unequivocal statement;
- The statement is from both parties;
- There has to be an action arising from it.
East Africa Power & Dandora Quarries
The Late Justice Channan Singh considered recitals for the basis …
“A recital especially one relating mainly to the history of the relationship and reasons for entering into an agreement, is not a term of a contract although it arises of ambiguity in the operative part a recital may be used to resolve the parts of that ambiguity.”
The Plaintiff sued the defendant on a mini consumption agreement for the supply of electricity under which the defendant undertook to pay the minimum annual charge of KShs. 12,840/- for a period of 46 months beginning 1st January 1965. The defendant did not dispute the agreement but claimed that it was void and unforceable for the following reasons:
1. There was no consideration;
2. It was illegal and not in accordance with the charging provisions of the Electric Power Act;
3. Plaint disclosed no cause of action because the plaintiff had at the material time no licence under the said Act;
4. The Plaintiff argued that the Defendant was estopped from denying the consideration which was stated in the Agreement as being a request by the defendants that the Plaintiff company should carry out certain works towards the installation of an electrical energy supply in return for which the defendant agreed to sign the minimum consumption agreement.
The defendant challenged the Evidence of the plaintiff in regard to a licence to generate or supply electricity. As a matter of fact the plaintiff did not remit original licences or renewals of the licence.
The court held that there was no estoppel operating to prevent the defendant from challenging the considerations stated in the recitals to the Agreement but on the Evidence that the plaintiff had shown that there was good consideration. And also there was no evidence to rebut the presumption that the licence granted to the Plaintiff company had been renewed at the proper time, place and proper procedure. (presumptions of regulation).
Grier V. Kettle
Judgment of Judge Russell on recitals
as the basis for Estoppel.
ESTOPPEL BY AGREEMENT
This is a rule of evidence whereby two or more persons have expressly or impliedly agreed that their legal relations shall be based on the assumption that a particular state of facts exists. Those parties are precluded from denying the existence of the assumed facts. An example of this kind of Estoppel is found in S. 121 of the Evidence Act the Estoppel of a tenant or a licencee. It says that no tenant is allowed to deny that at the commencement of the tenancy that his landlord had title to the property. The section deals with both estoppel of tenant and estoppel of licensee.
Rodseth V. Shaw 
This involved a tenancy for residential tenancy and when the landlord gave the tenant notice to quit at a particular time, the tenant sought to introduce circumstances that had prevailed ten years prior to the commencement of the lease which circumstances incapacitated the landlord from leasing out the premises. What in effect the tenant was saying was that the landlord never had title and could not have leased out the
The court held that a tenant cannot deny that the landlord had title to grant the lease at the commencement of the tenancy if he accepts the agreement or in other words becomes a persons tenant then he is deemed to acquiesce in the landlord’s want of title.
Ravi Bin Mohammed v. Ahmed  E.A. 782
Ahmed was a subtenant and he managed to buy the premises for which he was a sub tenant. The tenant of the main landlord continued asking Ahmed for rent and the question arose as to whether the first tenant could insist on getting rent from Ahmed on the basis of S. 121. The court held that NO that first tenant could not continue asking Ahmed for rent because Ahmed was not estopped from pleading and proving that his landlord’s title had been determined. In the words of the Court Estoppel prevents a tenant from disputing a landlords title at the time of granting the lease not subsequently thereafter. That fact is borne out of the wording of Section 121 to the effect that … “No tenant of immovable property, or person claiming through such tenant, shall, during the continuance of the tenancy, be permitted to deny that the landlord of such tenant had at the beginning of the tenancy a title to such immovable property; and no person who came upon any immovable property by the licence of the person in possession thereof shall be permitted to deny that such person had a right to such possession at the time when the licence was given.”
NO PERSON WHO CAME UPON ANY IMMOVEABLE PROPERTY BY THE LICENCE OF THE PERSON THEREOF SHALL BE PERMITTED TO DENY THAT SUCH A PERSON HAD A RIGHT TO SUCH PROPERTY.
A Licensee will not be allowed to deny that the licensor had the right to the property to which the licence was granted. (Licence is the relationship between a licensor and licensee)
Under S. 122 - there is the Estoppel of Acceptor of a Bill of Exchanged
S. 122. “ No acceptor of a bill of exchange shall be permitted to deny that the drawer had authority to draw such bill or to endorse it:
Provided that the acceptor of a bill of exchange may deny that the bill was in fact drawn or endorsed by the person by whom it purports to have been drawn or endorsed.”
It is to the effect that no acceptor of a bill of exchange shall be permitted to deny that the drawer had authority to draw such a bill or to withdraw such a bill or to draw it. The Acceptor is the financial institution and the drawer is the person that writes out the bill of exchange or other negotiable instrument. It is important to point out that the Bank or Financial Institution can deny the fact that the cheque was drawn by the right person, but the acceptor should not deny the drawer the right to draw. If the Bill of Exchange is a forgery it is upto the bank to prove it.
S. 123 deals with a variety of estoppels by agreement. The one being between the licensor and licensee, bailor and bailee, principal and agent. No licensee is permitted to deny that the licensor had a right to possession of property when the licence was given. Under this section no bailee will be permitted to deny that the bailor was entitled to the goods at the time he entrusted them to him. If you are a bailee you will not be allowed to deny that the bailor was entitled to the goods when they were given to you. The bailee can however show that he was compelled to deliver the goods to a person who had a right to them as against the bailor. The bailee can also show that the bailor without the bailee’s notice obtained notice from a third party who has now claimed the goods from the bailee (in case of a court order where the goods have been contested and the person with a superior right may have given the bailor notice that they will collect the goods and if the notice is not contested then they can have the goods). There can be third parties who can have superior titles to that of the bailor.
PRINCIPLE & AGENT ESTOPPEL
This is to the extent that if you are an agent to whom any goods have been entrusted, you will not be permitted to deny that the principal was entitled to the goods at the commencement of the principal/agent relationship. This is provided for in S. 123. If one is an agent and a person with a superior title gets and order you may be compelled to give the goods to the third party.
ESTOPPEL BY CONDUCT
The conduct should be such as to cause or permit a person to believe a thing to be true and the person must have acted in some way on this belief. That person must have acted in that belief either in doing or omitting to do something thereby altering his position to his detriment.
Hopgood v. Brown  1 ALL ER 450
In this case the Judge said “where one person the representor has made a representation to another person the representee in words or by acts or conduct or being under a duty to speak or act by silence or inaction with intention actual or presumptive and with the result of inducing the representee to alter his position to his detriment the representor in any litigation which may afterwards take place between him and the representee, the representor is estopped as against the representee from making or attempting to establish by evidence any averment substantially at variance with his former representation if the representee at the proper time and in the proper manner objects thereto. It is important to compare Lord Evershed statement with what is contained in S. 120 under this section one need not have acted to their detriment, suffice it that they acted.
The requirement for estoppel by conduct can be summarised as follows
1. Representation must be made with the intention that it be acted upon, it must be a wilful intention.
2. Under the Rule in Hopgood it would go further where you are under a duty to speak, act or take care, if you make a negligent statement you will be estopped from denying the statement’s truth or if you are under a duty to act and you don’t take any action then you would be estopped. You could make a positive representative in the sense that you were expected to act or speak and you didn’t. This failure would be what people relied on and it could give rise to estoppel.
Greenwood V. Martin’s Bank 
A husband and wife had a joint account in Martins bank and the bank undertook to honour cheques signed by both signatories. Afterwards the account was closed and an account opened in the sole name of the husband the wife having no authority to draw cheques on that account of the husband. During all this time the wife repeatedly forged her husband’s signature to the cheques and drew out money which she applied to her own uses. The husband became aware of these forgeries but was persuaded by the wife to say nothing about them. He kept quiet for 8 months when he finally decided to report the forgeries. The wife committed suicide. The husband then brought a suit against the bankers to recover the sums paid out of the sole account on cheques to which his signature had been forged. The court held firstly the Plaintiff owed a duty to the defendant bank to disclose the forgeries when he became aware of them as this would have enabled the bank to take steps to recover the money wrongfully paid to the wife. Secondly, through his failure to fulfil this duty, the bank was prevented from bringing an action against the plaintiff and his wife for the tort committed by the wife and thirdly, he had only brought the matter forward after the death of the wife. The plaintiff was estopped from asserting that the signatures from the cheques were forgeries and consequently he was not entitled to recover the money that he was seeking from the bank.
The second requirement is that the representation must be clear and unambiguous. This is to enable the parties to exactly know the import of the situation.
Century Automobiles v. Hutchings Biemer 
One of the statements made is that the level of precision should not be a lawyer’s statement.
The representation must be one of fact.
Fourthly the representation must not have the effect of sanctioning something prohibited by law. Income Tax Commissioners v. A.K. 
The Judge pointed out that no estoppel whatever its nature can operate to annul statutory provisions because it is statutory duty to obey the law.
Chatrath v. Shah  where it was stated that the doctrine that there can be no estoppel against a statute simply means that an estoppel cannot render valid something which the law makes invalid so that if a statute declares a transaction to be invalid or expressly declares that something should not be done, then estoppel cannot be used to override the specific directions of the law.
Promissory Estoppel is an exception to the general rule. It deals with the future state of affairs and occurs where a person makes a representation to another about the state of their future legal relations or their future conduct and the other person acts upon that. In this instance, an equitable estoppel arises such that the representor is estopped from denying the representation.
Nurdin Bandali v. Lombank Tanganyika Ltd.
In this case a lorry was bought on hire purchase terms. Buyer was late in one of the payment but when he later presented the money to the seller, it was later accepted. Just before he completed paying off the sums owing on the lorry, he was again late in depositing the payments. The Hire Purchase company seized the lorry and sought to sell it to recover the unpaid balance. The question arose as to whether the sellers had by accepting payments late waived their rights under the Hire Purchase Agreement. Consequently was the Hire Purchase Company estopped from falling back on the Hire Purchase Agreement. It was held that no waiver or estoppel arose on the facts of the case. But the court recognised that promissory estoppel did indeed exist in East Africa in the Judges view, the word thing, used in S. 120 was capable of wide interpretation and could comprise an existing state of affairs, legal relationships or future conduct. And in stating that, the Court relied on the High Trees case Central London Property Trust Ltd. V. High Trees House Ltd KB 134
In this case, by lease under seal dated September 24th 1937 the Plaintiff let to the defendant a block of flats for a term of 99 years with effect from 29.9.1937 at a rent of £2500 per annum. Owing to the second world war, in the early part of the 1940’s only a few of the flats were let, and it became apparent that the defendant would be unable to pay the rent reserved. After negotiations between the directors of the two companies, on 3rd January 1940, a letter was written by the plaintiff to the defendant confirming that the rent for the premises would be reduced from £2500 to £1250 essentially by half as from the beginning of the term. The Defendant paid the reduced rent. By the beginning of 1945 all flats were let out and in September of 1945 the Plaintiff wrote to the Defendants claiming that rent was payable at the rate of £2500. Thereafter, the Plaintiff initiated some friendly proceedings to claim the difference in rent for September to December 1945 quarter. In their defence the defendants pleaded that the agreement for the reduction of rent operated for the whole term of the lease and the plaintiff was estopped from demanding rent at the higher rate. It was held that where parties enter into an arrangement which is intended to create legal relations between them and in pursuance thereof one party makes a promise to the other, which he knows will be acted upon, and which infact is acted upon by the promisee, the court will treat the promise as binding on the promisor to the extent that it will not allow him to act inconsistently with it even though the promise may not be supported by consideration in the strict sense. The effect of the arrangement may be to vary the terms of the contract under seal by one of less value.
The second holding was that the arrangement between the parties in 1945 was one which fell within the first category, i.e. where you made a promise and were bound by the promise and so the agreement of the promise was bound on the promisee but it only remained operative so long as the conditions giving rise to it continued to exist and once those conditions ceased to exist in 1945 the plaintiffs were entitled to recover the full rent claimed at the rate reserved by the lease document.
In Century v Hutchings the issue of promissory was also discussed
(a) There must be a clear and unequivocal representation.
(b) There should also be an intention that it is acted on.
(c) There has to be action upon the representation in the belief that it is true.
Authorities are not in agreement but essentially that estoppel could be a principle of procedure and it could have aspects of substantive law where it could debar a person from raising a defence open to them. So you can have estoppel as a rule of procedure or as substantive law. The case of Law v. Bouvaries Estoppel is perceived as an aid to prove not as being essentially a principle on which you could found a case but in Canada v. Dom the court felt that Estopel could be viewed as substantive rule of law.
Combe v. Combe discusses these elements on what the place of estoppel in law is, is a rule of evidence or substantive law.