Duncan McNiven v Isla Jane McNiven & Ors

Proprietary estoppel requires an assurance or representation, reliance, and substantial detriment caused by that reliance. The central question is whether it would be unconscionable to allow the assurance to be disregarded. Detriment is assessed in the round, including relevant benefits received by the claimant.

Where an equity is established, the usual starting point is to hold the promisor to the assurance. The remedy may be reduced where full performance would be out of all proportion to the detriment. The court must select a proportionate remedy that does justice between the parties. On the facts, the appropriate remedy was the promised property interest less a quantified allowance for mortgage payments made by the promisor.

The claimant and defendants were adult siblings disputing their late mother’s property, 138 Queen’s Road, Tewksbury. The claimant had originally acquired the property jointly with his parents and later agreed that legal title would be transferred into his mother’s sole name for tax reasons.

The claimant contended that his mother had assured him that the property would ultimately be his and that he would continue paying the mortgages. He claimed a beneficial interest based on the 1993 agreement and proprietary estoppel. The defendants disputed the agreement, the claimant’s mortgage contributions and the extent of any entitlement.

The central issues were the ownership and severance of the beneficial joint tenancy, whether proprietary estoppel was established, and the appropriate remedy.

1. The claimant retained a 50% beneficial interest in the property after the 1993 transfer of legal title into his mother’s sole name. The transfer, together with the agreement that he would continue paying the mortgages and receive the property on her death, severed the equitable joint tenancy because it constituted a course of conduct inconsistent with continued joint tenancy.
2. Proprietary estoppel requires an assurance or representation, reliance and detriment. The underlying requirement is unconscionability. Detriment must be substantial, but it need not be financial. The court must assess the detriment in the round and take account of benefits received by the claimant: Thorner v Major [2009] UKHL 18, [2009] 1 WLR 776; Gillett v Holt [2001] Ch 210; Winter v Winter [2024] EWCA Civ 699.
3. The claimant proved repeated assurances that the property would be his on his mother’s death, reliance through assuming responsibility for the mortgages and allowing his mother to remain in the property, and substantial detriment. His temporary failure to meet payments did not remove unconscionability, viewed against the substantial payments made over the mortgage term.
4. The remedy had to be proportionate. The starting point was fulfilment of the promise, but the court considered the mortgage payments made by the claimant’s mother and applied the approach in Guest v Guest [2022] UKSC 27. The claimant was entitled to the net sale proceeds, subject to a deduction of £13,310 retained by the estate to reflect those payments.