[2025] EWHC 2054 (Ch)

It is common ground that the correct approach to the determination of the relief to be granted when a proprietary estoppel has been established, as explained by the Supreme Court in Guest v Guest [2024] A.C. 833, is the prevention or undoing of unconscionable conduct, not expectation fulfilment or detriment compensation. In many cases, once the equity is established, the fulfilment of the promise is likely to be the starting point, although considerations of practicality, justice between the parties and fairness to third parties may call for a reduced or different award (per Lord Briggs at [94]).

I have determined that the repudiation of Alan’s promise was unconscionable. I therefore start with the assumption, but not presumption, that the simplest way to remedy the unconscionability is to hold Alan’s estate to the promise: Guest v Guest at [75]. This in turn involves consideration of the nature of the promises and assurances made by Alan to Richard on which Richard relied to his detriment.

If Simon and George, as Alan’s executors, are able to show that the specific enforcement of the promise, or monetary equivalent, would be out of all proportion to the cost of the detriment to Richard, the court may limit the extent of the remedy. As Lord Briggs stated in Guest v Guest at [76], it will be a very rare case where the detriment is equivalent in value to the expectation and there is nothing in principle unjust in full enforcement of the promise being worth more than the cost of the detriment. Lord Briggs gives as examples of a remedy being out of all proportion to the detriment (i) a promise by an elderly lady to leave her carer a piece of jewellery if she stayed on at very low wages, which turned out on valuation by her executors to be a Faberge worth millions and (ii) a promise to leave a generous inheritance if the promisee cared for the promisor for the rest of her life, but where she unexpectedly died two months later.

There is more scope for departure from full enforcement of the promise if either or both of the promise and the detriment are not precisely defined by the time when the promise is repudiated: Guest v Guest at [77]. In the end, the court needs to consider its provisional remedy in the round, against all the relevant circumstances, and ask itself whether it would do justice between the parties, and whether it would cause injustice to third parties. The yardstick for that assessment is whether, if Alan had conferred the proposed remedy upon Richard, he would be acting unconscionably. The remedy should be sufficient only to enable the court to answer that question in the negative: Guest v Guest at [80].