Real property, real impact: What is the point of proprietary estoppel?

Article by Alice Hawker and Benedict Evans, 22^nd June 2026

This article was originally published by Estates Gazette here.

“One day, all this will be yours.” In varying guises, this story is familiar: a promise of land, acted on by the promisee to their detriment but later resiled from by the promisor. In such circumstances, equity may step in with a remedy.

While the doctrine is well-known, the question remains: what is the point of proprietary estoppel? Is the essential aim: (a) to give effect to the claimant’s expectation; (b) to ensure that detriment suffered by the claimant is compensated; or (c) something else? It was this question which vexed the Supreme Court in Guest v Guest [2022] UKSC 27; [2023] EGLR 2.

Family matters

The fact pattern in Guest was, in many respects, typical of the farm-inheritance cases that have played such a significant part in the emergence of proprietary estoppel. Son farmed the family farm for decades in reliance on father’s promise that he would inherit a sufficient portion of the farm to enable him to continue farming once his parents had died. Father and son fell out, and son was cut out of father’s will in favour of his two siblings.

The sole question for the Supreme Court was the correct approach to the remedy. The trial judge ordered the parents to pay an immediate lump sum representing the monetary equivalent of what son had been promised. The Court of Appeal upheld that remedy as within the trial judge’s wide discretion. 

Lord Briggs’ judgement on behalf of the majority (Lady Arden and Lady Rose concurring) considered that prior case law focused on upholding the claimant’s expectation rather than compensating the detriment suffered by the claimant in reliance, and concluded that there was “no good reason” for changing course now. Thus, the detriment in focus is not the detriment already suffered by the promisee but rather the detriment that would be suffered if the promise were resiled from (in contractual language, the expectation interest). The majority said: “The simplest way to remedy the unconscionability constituted by the repudiation is to hold the promisor to the promise.”

Having set out that starting point, Lord Briggs introduced numerous caveats and detours: a proportionality cross-check (“the remedy should not, without some good reason, be out of all proportion to the detriment, if that can readily be identified”); discounts for acceleration; and a list of examples of good reasons to depart from enforcing the promise, such as reluctance to enforce co-habitation, a need for a clean break, interests of third parties, and changed circumstances. Lord Briggs also said that, where there is more than one appropriate remedy, the promisor ought to be able to decide which remedy he prefers: “Since the aim of the remedy is to prevent or remove unconscionability, then where there are two different ways of doing so the persons against whom the equity is asserted should in principle be the ones to make that choice.”

On that basis, the majority upheld the trial judge’s focus on giving effect to the promise (albeit in monetary terms), but allowed the appeal on the basis that the trial judge had not discounted for acceleration, and gave the father the choice between a lump sum remedy or the transfer of land into a trust for son subject to a life interest in favour of his parents.

Lord Leggatt (with Lord Stephens concurring) agreed with protecting the promisee from the detriment suffered if the promise is resiled from, and that the most obvious way to do so is to compel performance. However, Lord Leggatt then said that an acceptable alternative to compelling performance is “to prevent the detriment that would otherwise flow from the failure to perform the promise by awarding compensation which puts B into as good a position, as best money can do it, as if B had not relied on A’s promise: in other words, to grant a remedy which compensates B’s reliance loss”. The equating of reliance loss with the detriment that would be suffered if the promise were not performed is a key departure from the majority view, which distinguished the two.

Lord Legatt continued, saying that the court should adopt whichever remedial approach imposes the least burden on the defendant, with the consequence that the claimant would effectively be capped at the lower of the expectation or the reliance interest. To illustrate how the court might go about valuing the “reliance loss”, Lord Leggatt included an appendix which sought to identify what son would have earned had he pursued other opportunities, what tax (including council tax) he might have paid, and how he might have invested his money.

How has Guest been applied?

Two key questions emerge for courts seeking to apply the guidance in Guest.

First, what does it look like to give effect to the promise? This came into focus in Armstrong v Armstrong [2025] EWHC 2054 (Ch), where the promise did not address the apportionment of debt between parts of the promisor’s farmland, leaving the judge to fall back on considerations of what the promisor could have decided that would not have been unconscionable.

Second, what falls within the wide range of reasons that justify departing from giving effect to the promise? An emerging category of cases where the court is likely to find good reason to depart are contracts for the sale of land that prove to be unenforceable for lack of compliance with section 2 of the Law of Property (Miscellaneous Provisions) Act 1989. For example, in Conway v Conway [2025] EWHC 33314 (Ch) the judge overturned the trial judge’s order for specific performance of the oral contract and remitted the matter to the County Court to determine “compensation for unjust enrichment”, seemingly on the basis that this was the only remedy pleaded in the alternative. In Thandi v Saggu [2023] EWHC 2631 (Ch); [2023] PLSCS 175, Rajah J likewise declined to provide a remedy based on the expectation interest and instead partially compensated the reliance loss. Interestingly, the judge there took each item of reliance loss in turn and considered whether it would be unconscionable not to remedy that particular loss.

A further example of departing from enforcement of the promise is Spencer v Spencer [2023] EWHC 2050 (Ch) where the court found that the prospects of exploiting mineral rights in part of the subject farmland (which was not in the promisor’s contemplation when making the promise) constituted a good reason for not enforcing the promise in whole.

Given the number and breadth of Lord Briggs’ caveats and workarounds, we anticipate this being a fertile source of argument for defendants.

What next for proprietary estoppel?

It was hoped that a Supreme Court judgment on proprietary estoppel would provide clarity and certainty for the doctrine. While cases like Winter v Winter [2024] EWCA Civ 699; [2024] EGLR 34 illustrate the Guest approach resulting in a clearer task for the trial judge and a more straightforward outcome (at least than a reliance loss valuation à la Lord Legatt’s appendix), the seminal judgment leaves open myriad arguments for something other than enforcement of the promise. We predict, therefore, that these claims will remain hard fought and difficult to predict on remedy.

In particular, we still expect defendants to focus on the detriment suffered in reliance on the promise, both to say that enforcing the promise would be disproportionate and as an alternative remedy if they can identify good reasons not to enforce the promise. Claimants are likely to want to avoid such focus – particularly in the level of detail needed to carry out a valuation exercise of the type illustrated by Lord Leggatt’s appendix. Given the proportionality cross-check in the majority’s approach, it remains unclear whether one can avoid such detailed scrutiny of the detriment suffered in reliance on the promise.

Any claim in proprietary estoppel will, of course, base its arguments as to remedy on Guest. However, rather than eliminating or reducing the scope of the arguments as to remedy, Guest has instead provided a framework through which those arguments are likely to take place.