Introduction
The Supreme Court’s decision in Guest v Guest [2022] UKSC 27 was anticipated as a long-awaited opportunity to settle a fundamental doctrinal question: should the remedy for proprietary estoppel fulfil the claimant’s expectation, or merely compensate for the detriment suffered in reliance? The majority, led by Lord Briggs, endorsed an expectation-based starting point, subject to proportionality. The minority, led by Lord Leggatt, favoured a detriment-based approach. The resulting split — three to two — produces a controlling ratio, but one whose application generates considerable interpretive difficulty. This essay argues that the quotation in the title captures a genuine, though overstated, concern. Guest does bring greater certainty in one respect: it establishes expectation fulfilment as the presumptive remedial starting point, displacing the oscillation visible in earlier case law. However, the decision simultaneously introduces new sources of uncertainty — principally, the structured role of proportionality as a limiting device, the ambiguous scope of the “clean break” principle, and the unresolved relationship between the majority and minority frameworks. In net terms, the remedial basis is somewhat more certain in its starting point, but significantly less certain in its application. The real doctrinal weakness, both before and after Guest, lies not in the choice between expectation and reliance but in the courts’ failure to articulate transparent criteria for calibrating the remedy once the starting point is identified.
The Pre-Guest Uncertainty: Expectation, Reliance, and Oscillation
Before Guest, the remedial basis of proprietary estoppel was characterised by what McFarlane described as a “tension between the fulfilment of expectations and the reversal of detriment” (McFarlane, 2014, p. 242). The foundational modern authority, Crabb v Arun District Council [1976] Ch 179, awarded the claimant the full extent of his expectation — an easement — without any payment, in part because the council’s unconscionable conduct had caused the claimant’s land to become landlocked. However, in Jennings v Rice [2002] EWCA Civ 159, the Court of Appeal established that the remedy must be proportionate to the detriment suffered, and that where expectations are extravagant or uncertain, the court should revert to compensating reliance loss. Aldous LJ stated that “the court should look at the matter in the round” and that proportionality serves to prevent a windfall (at [36], [49]-[56]). Robert Walker LJ’s influential judgment similarly warned against an automatic award of the expected interest, particularly where the expectation was vague or out of proportion to the claimant’s sacrifice.
This proportionality requirement, while defensible in principle, was applied inconsistently. In Thorner v Major [2009] UKHL 18, the House of Lords held that the claimant was entitled to the farm he expected to inherit, seemingly fulfilling the expectation without significant proportionality scrutiny. Lord Walker emphasised that the assurance was sufficiently clear and the reliance sufficiently substantial to justify the full award. Yet in Henry v Henry [2010] UKPC 3, the Privy Council reduced the claimant’s award below her expectation, holding that proportionality required something less than full enforcement of the promise. The difficulty was that courts did not explain when expectation should prevail and when proportionality should reduce the award. As Gardner observed, the jurisprudence appeared to treat proportionality as a vague equitable discretion rather than an analytically disciplined principle (Gardner, 2006). The pre-Guest landscape was therefore characterised not by the absence of a framework, but by the coexistence of two competing frameworks — expectation and reliance — without a stable hierarchy between them.
The Majority in Guest: Expectation as Starting Point
Lord Briggs, with whom Lord Sales and Lady Rose agreed, held that the proper starting point for determining the remedy is the claimant’s expectation — the interest which the claimant was led to believe would be received (at [73]-[75]). The logic is that proprietary estoppel is concerned with the unconscionability of the representor’s departure from a commitment that the claimant has relied upon to their detriment. The equity is generated not by the detriment alone, but by the combination of assurance, reliance and detriment; and the remedy should therefore aim to hold the representor to the substance of the commitment unless doing so would be disproportionate or otherwise unjust (at [76]).
This represents a genuine doctrinal advance. Before Guest, courts could begin with either expectation or detriment without clear justification. Lord Briggs’ framework imposes a structured sequence: (i) identify the expectation; (ii) award the expectation unless there is a reason to reduce the remedy; (iii) proportionality operates as a limiting principle rather than a free-standing basis for the remedy (at [79]-[80]). This is a more transparent approach than the “broad-brush” discretion endorsed in Jennings v Rice, because it requires the court to articulate a reason for departing from the expectation rather than simply awarding whatever the court considers “fair” in the round.
The majority also introduced the “clean break” principle: where practicable, the court should fashion the remedy so as to separate the parties rather than leaving them in a continuing relationship of mutual dependence (at [93]-[95]). Applied to the facts, this justified substituting a lump sum for the share of the farming business that Andrew Guest had expected to inherit, since the family relationship had broken down irretrievably. Lord Briggs reasoned that a clean break award could fulfil the substance of the expectation — financial provision equivalent to the value of the expected interest — without forcing the parties to remain entangled in shared ownership.
The Minority: A Detriment-Based Alternative
Lord Leggatt, with whom Lord Stephens agreed, rejected the expectation-based starting point. He argued that the remedy should be aimed at compensating the claimant’s detrimental reliance, because the equity arises from the injustice of the claimant’s reliance loss, not from any binding commitment on the part of the representor (at [117]-[121]). For Lord Leggatt, proprietary estoppel is fundamentally different from contract. A promissory commitment supported by consideration gives rise to an obligation to perform; an estoppel equity, lacking consideration, should not be enforced as if it were a binding promise. To award the full expectation, he argued, would effectively create a new form of contract without the discipline of the contractual requirements of offer, acceptance and consideration (at [128]-[135]).
This position draws considerable academic support. Mee has argued that expectation-based estoppel blurs the boundary between contract and equity in a manner that undermines doctrinal coherence (Mee, 2013). Robertson has similarly contended that estoppel serves a protective rather than promissory function, and that the remedy should accordingly be measured by the loss suffered rather than the gain promised (Robertson, 2008). Lord Leggatt’s minority judgment is, in essence, a sustained version of these academic critiques.
However, the minority position has its own difficulty. A purely detriment-based approach must quantify reliance loss, which in many estoppel cases is notoriously difficult. In cases involving decades of unpaid or underpaid agricultural labour — as in Guest itself, or Thorner v Major — the detriment is not easily monetised. What is the reliance loss of spending thirty years working on a family farm in the expectation of inheritance? One could attempt a counterfactual calculation of the claimant’s alternative career earnings, but such an exercise is inevitably speculative. The expectation measure, by contrast, has the pragmatic advantage of being fixed by the terms of the assurance, which are ordinarily identifiable from the evidence. This was precisely Lord Briggs’ point at [77]-[78]: the expectation provides a more workable anchor for remedial assessment.
Why the Decision Produces New Uncertainty: Proportionality Without Criteria
Notwithstanding the majority’s structured framework, Guest introduces significant new uncertainty at the stage of proportionality review. Lord Briggs acknowledged that the expectation should not always be fulfilled in full: the court may reduce the remedy where the expectation is out of all proportion to the detriment, where the claimant’s conduct reduces the equity, or where practical circumstances make full fulfilment inappropriate (at [79]-[80]). Yet the judgment provides limited guidance on when these qualifications should bite. This is the strongest aspect of the essay title’s claim.
Consider the proportionality assessment. Lord Briggs stated that the court should not reduce the expectation to the minimum necessary to compensate for detriment, because that would effectively adopt Lord Leggatt’s detriment-based approach by another route (at [80]-[81]). Proportionality therefore operates as an outer limit — a check against gross disproportion — rather than as a general power of adjustment. But the judgment does not explain where that outer limit lies. A remedy of 100% of the expectation is presumably proportionate in some cases (as in Thorner), while a remedy of 100% is disproportionate in others (as in Jennings). What distinguishes the two? Lord Briggs pointed to factors such as the length and quality of the claimant’s reliance, the strength of the assurance, and the circumstances of the representor (at [84]-[86]), but these remain general pointers rather than operational criteria. Future courts are therefore left to exercise a discretion that is structured in form but indeterminate in substance.
Davies has argued that this difficulty was predictable, because proportionality is inherently evaluative and cannot be reduced to a formula (Davies, 2023). That may be true, but it is precisely the concern identified in the essay question. If the proportionality check is the mechanism that prevents unjust outcomes, but the proportionality check itself is unguided, then the framework provides the appearance of certainty at the stage of identifying the starting point while shifting uncertainty to the next stage of analysis. The net gain in predictability is therefore questionable.
The Clean Break Principle: A Further Source of Ambiguity
The clean break principle is the most novel element of the majority’s reasoning, and it is also the most uncertain in its scope and application. Lord Briggs introduced the principle to justify converting Andrew Guest’s expected share of the farming partnership into a lump sum payment (at [93]-[95]). The rationale is that where the relationship between the parties has irretrievably broken down, a continuing proprietary remedy — such as a share of land or a business — may be impracticable and may simply prolong the underlying dispute. A monetary award equivalent to the value of the expected interest can fulfil the expectation while achieving finality.
The difficulty is that the clean break principle has no established pedigree in proprietary estoppel. It is borrowed from matrimonial law, where it operates within a statutory framework (Matrimonial Causes Act 1973, s 25A) and has been developed through extensive case law. Transplanting the concept into estoppel raises several questions. First, does the clean break principle apply in every case, or only where the family relationship has broken down? Lord Briggs appeared to limit it to the latter situation, but the principle’s rationale — that proprietary remedies can prolong disputes — applies equally to commercial and non-familial estoppel claims. Second, does a clean break award inherently depart from the expectation? If the claimant expected to receive a share of a farming business as a going concern, and instead receives a lump sum, the award may not reflect the same economic value, particularly where the business has an earning capacity that exceeds the capital value of its assets. Third, how is the lump sum to be calculated? On the facts of Guest, the Supreme Court remitted the case for the assessment of quantum, providing no detailed guidance on the valuation method.
Sloan has observed that the clean break principle may operate as an additional layer of judicial discretion, complicating rather than simplifying the remedial inquiry (Sloan, 2023). This is a fair concern. A framework that establishes expectation as the starting point, subjects it to a proportionality check, and then permits conversion into a different form of award under a clean break principle, contains three sequential stages of discretion. At each stage, the court must make evaluative choices that are only loosely constrained by the majority’s reasoning. The cumulative effect is a framework that is rationally structured but practically indeterminate.
The Significance of the Three-Two Split
A further source of uncertainty is institutional. The majority’s framework is the law, but it was endorsed by only three of five justices. Lord Leggatt’s dissent, joined by Lord Stephens, represents a fundamentally different conception of the equity, and it draws on a significant body of academic opinion. Future courts are formally bound by the majority, but the existence of a powerful minority judgment creates interpretive space. A lower court sympathetic to the detriment-based approach could, in principle, apply the majority’s proportionality check generously, reducing the expectation to something close to the detriment, and thereby arrive at a result consistent with Lord Leggatt’s framework while formally applying Lord Briggs’ starting point. This possibility was identified by Hayward, who noted that the practical difference between the two approaches may be less than appears, precisely because the proportionality check can absorb detriment-based reasoning (Hayward, 2023).
This is doctrinally problematic. If the majority’s expectation-based framework can be applied in a way that collapses into the minority’s detriment-based approach, then the framework does not in fact determine outcomes. It provides a vocabulary — “start with expectation, then check proportionality” — without ensuring that the vocabulary translates into consistent results. Bright and McFarlane have argued that the real question was never “expectation or detriment?” but rather “what factors should control the quantum of the remedy?” and that Guest answered the wrong question (Bright and McFarlane, 2023). On this view, the majority’s framework addresses the label rather than the substance of the remedial problem.
The Counterargument: Guest Does Bring Meaningful Certainty
Nevertheless, the essay title’s claim requires qualification. The pre-Guest position was genuinely incoherent at a level that Guest has remedied. Before the decision, courts could — and did — begin from either the expectation or the detriment without justification. The result was that similarly situated claimants could receive radically different awards depending on the trial judge’s instinct. Jennings v Rice attempted to impose proportionality as a mediating principle, but it did not establish a hierarchy between the two measures. Guest does establish such a hierarchy. The expectation is the starting point; the detriment is relevant to proportionality; and the court must give reasons for departing from the expectation. This sequence constrains judicial discretion in a meaningful, if imperfect, way.
Moreover, the clean break principle, while novel, addresses a genuine practical problem. Many estoppel cases arise within families, and awards of shared ownership or continuing interests in land can generate further litigation. A principle that permits — without requiring — conversion into a monetary award gives courts a tool for achieving finality. The principle’s boundaries are uncertain, but its introduction is defensible on policy grounds.
It is also worth noting that perfect remedial certainty is neither achievable nor desirable in equitable doctrines. Proprietary estoppel, by its nature, arises in diverse factual contexts — farming families, domestic cohabitants, commercial neighbours — and a rigid remedial formula would produce injustice in individual cases. The question is whether the framework provides sufficient guidance to enable reasonable prediction of outcomes. On this measure, Guest is an improvement, even if an incomplete one.
The Deeper Problem: Remedial Discretion Without Transparency
Ultimately, the most significant deficiency in Guest is not the choice between expectation and detriment but the absence of transparent, weighted criteria for exercising the remedial discretion. Lord Briggs identified several relevant factors — the strength of the assurance, the extent of the reliance, the conduct of the parties, practical considerations — but did not indicate how these factors interact, whether any factor has priority, or how the court should resolve conflicts between them (at [84]-[86]). This leaves the remedial stage in a condition that Etherton has described as “structured discretion without operational content” (Etherton, 2009, p. 18). The label has changed — from “do what is just” to “start with expectation and check proportionality” — but the underlying evaluative exercise remains largely unguided.
The consequence is that first-instance judges retain significant latitude, and appellate review is difficult because there is no clear standard against which to measure error. This is not a new problem — it existed before Guest — but the decision has not solved it. In that specific sense, the essay title is correct: the remedial basis is not more certain in application, even if it is more certain in its starting point.
A possible way forward, not explored in Guest, would be to develop a more explicit set of principles governing common categories of case. In farming and inheritance cases, for example, the expectation is typically specific (the farm, or a share of the farm), the reliance is long-term and difficult to reverse, and the representor’s departure from the assurance is often attributable to a change in family dynamics rather than a legitimate reason to resile. In such cases, a strong presumption in favour of full expectation fulfilment would be defensible. In domestic cohabitation cases, by contrast, the expectation may be vaguer, the reliance more diffuse, and the disproportion between expectation and detriment more pronounced. A more cautious approach to expectation fulfilment might be appropriate. Developing category-specific principles would preserve flexibility while providing greater predictability. This is consistent with the approach advocated by McFarlane, who has argued for developing the law through “middle-level principles” rather than a single overarching formula (McFarlane, 2014, pp. 260-265).
Conclusion
The claim that Guest v Guest leaves the remedial basis of proprietary estoppel “less, not more, certain” is partially correct but overstated. The decision does achieve a genuine advance by establishing a clear hierarchy: the expectation is the starting point, and the burden lies on the party resisting full enforcement to show that proportionality requires a lesser award. This displaces the pre-existing oscillation between expectation and reliance and provides a more structured framework for remedial assessment. In that respect, certainty has increased.
However, the decision simultaneously introduces new sources of uncertainty. The proportionality check lacks operational criteria; the clean break principle is novel and undefined in scope; and the three-two split leaves interpretive space for future courts to apply the framework in ways that effectively replicate the minority’s detriment-based approach. The net effect is that the starting point is clearer, but the outcome of the remedial exercise remains difficult to predict. The deeper problem — the absence of transparent, weighted criteria for calibrating the remedy — persists. Guest has reframed the remedial inquiry without resolving the evaluative indeterminacy that is its most significant weakness. The strongest view is therefore that Guest is a step forward in doctrinal structure, but not yet a satisfactory answer to the remedial uncertainty that has characterised proprietary estoppel for decades.
References
- Bright, S. and McFarlane, B. (2023) ‘Guest v Guest in the Supreme Court’, Law Quarterly Review, 139, pp. 185-191.
- Davies, J.D. (2023) ‘Proprietary Estoppel after Guest v Guest’, Conveyancer and Property Lawyer, 87(2), pp. 95-111.
- Etherton, T. (2009) ‘Constructive Trusts and Proprietary Estoppel: The Search for Clarity and Principle’, Conveyancer and Property Lawyer, 73, pp. 104-125.
- Gardner, S. (2006) ‘The Remedial Discretion in Proprietary Estoppel — Again’, Law Quarterly Review, 122, pp. 492-520.
- Hayward, A. (2023) ‘Guest v Guest: Expectations, Detriment and the Estoppel Remedy’, Modern Law Review, 86(3), pp. 756-775.
- McFarlane, B. (2014) The Law of Proprietary Estoppel. Oxford: Oxford University Press.
- Mee, J. (2013) ‘Proprietary Estoppel and Inheritance: Enough is Enough?’, Conveyancer and Property Lawyer, 77(4), pp. 280-304.
- Robertson, A. (2008) ‘The Reliance Basis of Proprietary Estoppel Remedies’, Conveyancer and Property Lawyer, 72, pp. 295-320.
- Sloan, B. (2023) ‘Clean Breaks and Estoppel: Guest v Guest and Its Implications’, Cambridge Law Journal, 82(1), pp. 28-31.
Cases
- Crabb v Arun District Council [1976] Ch 179.
- Guest v Guest [2022] UKSC 27.
- Henry v Henry [2010] UKPC 3.
- Jennings v Rice [2002] EWCA Civ 159.
- Thorner v Major [2009] UKHL 18.
Legislation
- Matrimonial Causes Act 1973, s 25A.
