In this post, Tobias Seger, an Associate at CMS, comments on the Supreme Court’s decision in Guest v Guest [2022] UKSC 27, handed down by the Supreme Court on 19 October 2022. This case concerns the proper approach to granting relief under the doctrine of proprietary estoppel.


““One day my son, all this will be yours” Spoken by a farmer to his son when in his teens and repeated for many years thereafter.” This is Lord Briggs introduction to his judgment in Guest v Guest and this also summarises the facts at issue. As a result of this promise the son had lived and worked on his family’s farm for over 25 years, only earning a very small wage. Around 2008 there was a breakdown in the relationship between the father and son and as a result the son was removed from the will. The son applied to the court under the doctrine of proprietary estoppel to be awarded the farm that he was promised.

Proprietary estoppel applies where A (the promisor) makes a promise in relation to property to B (the promisee) and B relies on that promise to their detriment. A later reneges on that promise in a way that is unconscionable. In those circumstances B may have an action against A.

The court of first instance ruled that the son did have a valid claim on the basis of proprietary estoppel and ruled that the parents should sell the farm and the son should receive from the proceeds of sale 50% of the value of the farming business and 40% of the land and buildings of the farm (both payments to be made after tax). This was upheld by the Court of Appeal and subsequently appealed to the Supreme Court.

It was perceived that there was a “lively controversy” whether the remedy for a claim under proprietary estoppel should be compensation for the detriment suffered by the promisee or enforcement of the promise, as long as said enforcement would not be disproportionate.

Given the controversy, it is unfortunate Guest v Guest was decided in a 3-2 split decision, with two very persuasive judgments. The majority, following the judgment of Lord Briggs, ruled that the primary remedy should be enforcement of the promise, while the minority, following the judgment by Lord Leggat, argued that the remedy should be compensatory in nature. Nevertheless, the two judgments provide an extensive analysis of the relevant authorities, set out in more detail below and therefore provide a detailed review of the guiding principles going forward.

Legal Analysis

Lord Briggs (with Lady Arden and Lady Rose concurring) is of the view that when proprietary estoppel is engaged, the starting position is that the court should try to satisfy the promisee’s expectation, rather than compensating them for the detriment that they have suffered as a result of the promise being rescinded.

Lord Briggs analysed proprietary estoppel as something that stops the promisor from reneging on their promise. The court’s remedy is to hold the promisor to his original promise, similar to the doctrine of specific performance. His judgment stated that “the harm caused by the repudiation of the promise is not the same as the detriment suffered.” He noted that “[t]he true purpose, as recognised by the Court of Appeal in the present case, is dealing with the unconscionability constituted by the promisor repudiating his promise.” It is, in his view, wrong to treat that question as limited to the issue whether or not an equity arises and then not taking it into account when framing the remedy.

In summary, Lord Briggs argued that a court should approach a claim under proprietary estoppel in three stages:
(1) The court should determine whether the promisor’s repudiation is unconscionable.
(2) The second stage should start with the assumption that the simplest way to remedy the unconscionable repudiation is by holding the promisor to the promise.
(3) If the promisor can prove that the specific performance of the full promise, or monetary equivalent, would be out of all proportion to the cost of the detriment, then the court may consider to limit the remedy.

Lord Briggs concluded: “In my view therefore this court should firmly reject the theory that the aim of the remedy for proprietary estoppel is detriment-based forms any part of the law of England.”

On the other hand, Lord Leggat (and Lord Sales concurring with his judgment) focused on the fact that proprietary estoppel was originally based on the acquiescence by A in, or encouragement of, a mistaken belief by B that A had given them a property right. He stated that “[t]his understanding of the doctrine in negative and defensive terms, however, subsequently evolved into a conception of “proprietary estoppel” as a positive cause of action.” He suggested that this second form of proprietary estoppel would be better named a property expectation claim.

Lord Leggat emphasised that proprietary estoppel should be governed by principle and not just the conscience or sense of fairness of the individual judge. He argued that a property expectation claim does not operate in a binary way. The approach by the courts has not been that, provided there has been substantial reliance by the promisee, the promise will be enforced. Instead, there have been cases where a sum of money has been awarded to the claimant “which does not reflect, and was not intended to reflect, the value of what was promised.”

In terms of remedy, Lord Leggat agreed with Lord Briggs that the court can ask the promisor to perform the promise, however, in Lord Leggat’s view where there is more than one way to avoid detriment to the claimant the court should, in principle, adopt the remedial approach which imposes the least burden on the defendant. Lord Leggat’s principle position is therefore one where the court should seek to compensate for the detriment suffered by the promisee rather, as suggested by Lord Briggs, to hold the promisor to their promise.

Lord Briggs dismissed this view in his judgment stating that:

the supposed logic of the detriment-based approach is in my view both faulty in origin and wrong in its inevitable result. It is faulty in origin because it fails to recognise that while reliant detriment is necessary to engage the equitable relief, and forms a large part of its moral justification, it is the repudiation of the promised expectation which constitutes the unconscionable wrong.”

While both judgments provide a wide review of the case law in this area, they both focus on the proper interpretation of the term “minimum equity to do justice” coined by Scarman LJ in Crabb v Arun District Council [1975] EWCA Civ 7.

Lord Briggs argued that the analysis proposed by Scarman LJ is all about fine tuning the fulfilment of the exception of the promise and has nothing to do with valuing and then compensating for the detriment suffered by a disappointed claimant. He also cited the case of Baker v Baker [1993] EWCA Civ 17 in support of this argument where it was held that the remarks by Scarman LJ should not be interpreted to suggest that the court necessarily had to place the minimum value on the disappointed interest.

The majority therefore upheld the general approach taken by the court of first instance. However, Lord Briggs held that the judge of first instance failed to properly take into account that the promise was being accelerated by the fact that the parents were still alive and so the claimant would not have been able to inherit anything at this point, even if the promise was still in place.

Lord Briggs therefore allowed the appeal to that extent and provided the parents with a choice to either put the farm under a trust, with the parents having a life interest in the meantime or to provide the claimant with a financial compensation now (including an appropriate discount taking into account the acceleration).

Turning to the minority decision. A key argument by Lord Leggat was that the law has set out clear rules that are necessary to transfer property and a mere promise does not fulfil those conditions. He noted that “[d]escribing failure to keep such a promise as “unconscionable” cannot justify disregarding law laid down by Parliament.” He argued that the doctrine does not and could not sensibly have as its aim the enforcement of promises which do not satisfy the requirements for the creation of legal obligations.

He therefore concluded that the remedy must focus on the detriment suffered and when there are multiple means of avoiding detriment to the claimant the court should use whichever remedy imposes the least burden on the defendant.

While he does not believe that Scarman LJ intended to lay down any general principles when using, the phrase “the minimum equity to do justice” has since been used many times to denote a general application. To do justice to the defendant requires the court not to award a remedy which is more generous to the claimant and more burdensome for the defendant than is necessary to achieve the underlying purpose for which the remedy is granted.

He concluded, like Lord Briggs, that the court of first instance failed to properly estimate the claimant’s reliance on the loss and Lord Leggat therefore provided his own calculation in the appendix to the judgment which resulted in a sum of £610,000 to be awarded to the claimant. In the original judgment the claimant was to be awarded around £1.3m.


Following the majority judgment, the law has now been clarified in relation to the proper remedy for a claim of proprietary estoppel. However, due to the fact that it was a narrow split decision with two very persuasive judgments the UKSC may not have succeeded in their aim to settle the lively debate that was referenced in both judgments.

The key takeaway for claimants and practitioners alike is that cases in relation to proprietary estoppel will be highly fact specific. While the test set out by Lord Briggs will be very helpful guidance going forward the question whether or not the fulfilment of the full promise is proportionate will be key.

Furthermore, as seen by the outcome of this case the court will be at pains to ensure a fair outcome for all parties involved and try to ensure that the defendant also does not suffer unnecessarily.

Finally, when deciding the remedy, careful consideration needs to be taken when there is an acceleration of the promise. In those circumstances, both judgments agree, an appropriate discount in the award needs to be made.