‘One day this will all be yours’: when a promise overrides your Will

“One day, all this will be yours.” It is one of the most natural things a parent can say — across the kitchen table, in the yard, at the end of a long day in the family business. Said once, it is a hope. Said for twenty years to a son or daughter who stays on for modest pay and turns down other opportunities, it can become something the courts will enforce, whatever your Will says.

That is the doctrine of proprietary estoppel. For business owners, farmers and property families, it is one of the most important and least understood risks in estate planning. The good news is that it is almost entirely avoidable, provided what you say and what your Will says tell the same story.

What the rule actually is

In England and Wales you are free to leave your estate to whomever you choose. Proprietary estoppel is one of the exceptions. It allows a court to step in where it would be unconscionable — plainly unfair — for someone to go back on a promise about property. Three elements need to be present.

• Assurance. A promise or assurance that the person has, or will be given, an interest in property — a farm, a house, a share of a business. It does not need to be in writing, and it can be built up from repeated remarks over many years rather than a single conversation.
• Reliance. The person acted on that assurance. They stayed when they might have left, or shaped their working life around the promise.
• Detriment. Relying on the promise left them worse off in some real sense — years of low pay, a career given up, their own savings or labour put into the property.

If all three are present and the court considers it unconscionable for the promise to be broken, it can award the person an interest in the property or a sum of money, even if the Will leaves them nothing.

Guest v Guest — how the courts decide what to award

The leading case is Guest v Guest [2022] UKSC 27. Andrew Guest left school at 16 in 1982 and worked on his parents’ dairy farm, Tump Farm, for more than thirty years on relatively low wages. His parents had assured him that he would inherit a substantial share of the farm — enough to run a viable farming business. The relationship broke down, and in 2014 they made new Wills cutting him out.

The trial judge found in Andrew’s favour and ordered an immediate payment of around £1.3 million, calculated as 50% of the value of the farming business and 40% of the value of the farm land and buildings. In practice, the farm would have had to be sold to pay it.

The Supreme Court, by a majority, confirmed that the starting point is the promise itself: the court’s task is to undo the unfairness of the promise being broken, and the natural way to do that is usually to hold the promisor to it. But it also said that Andrew should not receive more, or sooner, than he had been promised. He had expected to inherit on his parents’ death — not to receive cash while they were still alive. So his parents were given a choice: either put the farm into trust so that Andrew would receive his share on their deaths, or pay him compensation now, reduced to reflect that he was receiving it years earlier than expected.

The lesson for families is sobering. The court was not rewriting a Will out of sympathy. It was holding parents to what they had said.

A more recent example — Winter v Winter

In Winter v Winter [2024] EWCA Civ 699, decided by the Court of Appeal in June 2024, three brothers had worked for most of their lives in their parents’ market garden business near Bridgwater in Somerset, which by then was run through a partnership and a limited company. The trial judge found that their parents had given assurances over many years that, if the sons committed their working lives to the business, it would ultimately be divided equally between them. After a falling-out, their father changed his Will in 2015 to leave his share of the business to one son alone. He died in 2017.

The other two brothers claimed. Their brother argued that they had suffered no real detriment — the trial judge had found they would not have built up as much wealth elsewhere. The Court of Appeal disagreed and upheld the award of a one-third share each of their father’s interest in the business. Where someone has made a life-changing choice and worked for many years in reliance on a promise, the court said, the loss of the chance to lead a different life can itself be detriment. It is not simply a sum on a calculator.

That matters for business owners in particular. It is not enough to say “but I paid them a fair salary”. If the promise shaped their life, the court may still hold you to it.

A worked example

Take a Sussex couple — we will call them Martin and Susan, purely as an illustration. Martin built up a successful building company over thirty years. Their son Tom joined at 19, turned down a place on a surveying degree, and has run site operations for two decades on a salary well below what he could earn elsewhere. For years, Martin has said at family gatherings, “The firm will be Tom’s one day — that’s the deal.”

Their daughter Emma lives in London and has never been involved. Recently, Martin and Susan have begun to feel that leaving the business to Tom alone would be unfair to Emma, and they are drawn to simply splitting everything equally in their Wills.

That instinct is understandable — but if they do it quietly, after two decades of promises to Tom, they are building a dispute into their estate. Tom may well have a proprietary estoppel claim, and Emma may find her inheritance tied up in years of litigation with her own brother. The very fairness they were aiming for could be the thing that divides the family.

The better route is to decide what is genuinely fair, talk to both children, and make sure the Wills reflect a plan everyone has heard. That might mean the company passing to Tom, with Emma receiving other assets or a balancing sum. It might mean shares being transferred to Tom during their lifetimes. Either way, it is a decision made in the open — not a surprise read out after the funeral.

The traps

• Casual promises add up. A remark here and there, repeated over years, can amount to an assurance. Courts look at the whole course of dealing, not one conversation.
• Changing your mind late. Many of these cases arise after a falling-out, when the Will is changed to reflect the new mood. If the promise has already been relied upon, a new Will may not be the end of the matter.
• Assuming salary settles it. As Winter shows, paying someone reasonably does not automatically remove the risk if the promise shaped their whole working life.
• Vague promises. “You’ll be looked after” or “the farm will stay in the family” can be argued over for years. Vagueness does not protect you; it simply makes the dispute harder to resolve.
• It is not only children. A long-serving employee, a partner’s child or a relative who has cared for you in reliance on a promise of a house can all bring a claim.

What to do

Say what you mean

If you intend a child to take over the business or the farm, say so clearly — and say what, if anything, depends on it. If you have not decided, say that too. “We haven’t decided yet, and it may change” is a perfectly honest thing to tell a child who is thinking about their future.

Put the promise in writing

Where a real commitment is being made, record it properly — whether through a shareholders’ agreement, a partnership agreement, a lifetime transfer of shares or a clear written understanding. Your Will then becomes the final piece of a plan that is already documented, rather than the only evidence of what you meant.

Align your Will with what you have told the family

The single most effective step is making sure your Will says what your family has been led to expect. Where your wishes have changed, the family should hear it from you while you are here to explain — not discover it at the reading of the Will.

Record your reasons

If you are treating children differently, or moving away from something you once said, tell us why when we take your instructions. We keep a careful note of your reasons on file. If a question is ever raised later, a clear contemporaneous record of your thinking is far more persuasive than anyone’s memory of a conversation.

Think about tax at the same time

Succession and tax planning belong together. From April 2026, Business Relief and Agricultural Property Relief give full relief on up to £2.5 million of qualifying assets combined, with 50% relief above that. How and when a business or farm passes to the next generation now matters more than ever, and a plan that settles the family question and the tax question together is far stronger than one that tackles either alone.

A promise is a plan — make it a deliberate one

Most parents who say “one day this will all be yours” mean it kindly. The problems arise when life moves on and the Will moves with it, but the promise does not. Keeping what you say and what you sign in step is one of the simplest and most valuable things you can do for the people who will carry on after you.

If you have made promises about the business, the farm or the family home — or you are not sure what you have committed to — book a Discovery Call. It takes 30 minutes, the fee is £30, and it is credited against your fees if you instruct us.