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Behind the terms: estoppel — when you cannot go back on what you promised — Articles

Estoppel is not a cause of action — you cannot sue someone for "estoppel". It is a shield: a doctrine that prevents a party from asserting a legal right or a fact that would be unjust given their earlier conduct or representations. The word comes from the Old French "estopper" — to stop up. Understanding estoppel can matter enormously in contract disputes, property cases, and informal arrangements.

Promissory estoppel: you promised not to enforce your rights

Promissory estoppel arises where: (1) a party makes a clear and unequivocal representation that they will not enforce a strict legal right; (2) the other party relies on that representation; and (3) it would be inequitable for the first party to resile from it. The foundational English case is Central London Property Trust v High Trees House [1947] KB 130, where Denning J held that a landlord who agreed to accept half rent during World War II could not later claim the full rent for the wartime period. Critically, promissory estoppel does not create new rights — it only suspends or extinguishes existing ones. And it is a "shield, not a sword" in English law — it cannot be used offensively to create a cause of action where none exists. See the estoppel glossary entry for the full definition.

Estoppel by representation: you stated a fact you cannot now deny

Estoppel by representation (or estoppel in pais) applies where a party makes a clear, unambiguous representation of existing fact (not a future promise), the other party relies on it to their detriment, and it would be unjust to allow the first party to deny it. Example: a seller represents that a property is freehold; the buyer relies on this and completes — the seller is estopped from asserting the property is leasehold. Unlike promissory estoppel, estoppel by representation can be used as a cause of action (as a sword) in some circumstances.

Proprietary estoppel: informal promises about land

Proprietary estoppel is particularly important in family property disputes and farming cases. It arises where: (1) a landowner makes an assurance about rights over their land; (2) the other party relies on that assurance (for example, by working on the farm unpaid, or by building on the land); and (3) the relying party suffers detriment. If established, the court has a wide discretion to fashion a remedy — which may be the full interest promised, or something less, depending on what is "proportionate to the detriment". The leading case is Yeoman's Row Management Ltd v Cobbe [2008] UKHL 55 (which narrowed its scope) and Thorner v Major [2009] UKHL 18 (which reaffirmed it for family farming situations). Claims based on verbal promises — "the farm will be yours when I die" — can succeed under proprietary estoppel even where the promise was never formalised.

Issue estoppel and cause of action estoppel: you cannot relitigate what is decided

These are procedural doctrines rather than substantive law. Cause of action estoppel prevents a party from relitigating a cause of action that has already been finally determined between the same parties. Issue estoppel prevents relitigation of a specific issue that was necessarily decided in prior proceedings between the same parties. Together they underpin the principle of finality in litigation — you get one fair opportunity to argue your case; if you lose, you cannot simply issue a new claim raising the same point. Related is the rule in Henderson v Henderson (1843), which requires a party to bring forward their whole case in one proceeding; failing to raise a point that could and should have been raised in earlier litigation may bar it from being raised later.

Practical significance

Estoppel most often arises in: informal property arrangements (especially inheritance expectations and farming partnerships); long-running commercial relationships where practices have varied from the written contract; landlord and tenant disputes where rent reductions were informally agreed; and situations where one party has invested substantially on the faith of another's promise. If you are in any of these situations, document everything — written records of representations and your reliance on them are essential to an estoppel claim. See also the contract glossary entry and the tort vs contract article for the wider legal context.

This article is for general information only and is not legal advice. Always check the official source and consult a qualified lawyer for your situation.

Promissory estoppel: you promised not to enforce your rights

Estoppel by representation: you stated a fact you cannot now deny

Proprietary estoppel: informal promises about land

Issue estoppel and cause of action estoppel: you cannot relitigate what is decided

Practical significance

Questions about this article