Why the law should recognise that when stepparents include stepchildren in mirror wills, there must be a deal.
One in three UK families is now “blended” – a term describing households where one or both partners have children from previous relationships. For these families, inheritance planning presents a unique challenge: how do you provide for your spouse while ensuring your own children aren’t left with nothing?
The answer, for many couples, is mirror wills. Each spouse leaves everything to the other, with the estate passing to all the children – biological and step – on the second death. It seems fair. It seems sensible. And it is devastatingly easy to exploit.
The Problem the Law Ignores
Mirror wills are not necessarily mutual wills. The distinction matters enormously. A mutual will creates a binding obligation – after the first spouse dies, the survivor cannot change the arrangement. A mirror will creates no such obligation. The surviving spouse is entirely free to rewrite their will, cutting out their stepchildren completely.
This is precisely what happened in McLean v McLean [2023] EWHC 1863. Reginald and Maureen McLean had been married for 45 years. In 2017, they made mirror wills leaving their estates to each other, then equally to their four children – three being Reginald’s from his first marriage. When the solicitor warned Reginald that Maureen could change her will after his death, he said he trusted her implicitly.
Reginald died in March 2019. By August 2019, Maureen had executed a new will cutting out all three stepchildren and leaving everything to her biological son. She died weeks later.
The stepchildren argued the wills were mutual. They lost. The court found that trust and expectation, however reasonable, did not amount to a binding agreement. The law required clear evidence of a contract not to revoke – and implicit understanding, however obvious, was not enough.
Maureen’s estate, including everything she had inherited from Reginald, passed entirely to her son. Reginald’s children received nothing from either parent.
The Question Nobody Is Asking
The McLean case represents the current state of the law. But it leaves a critical question unanswered: why would a stepparent ever include stepchildren in a mirror will if not as part of a mutual arrangement?
Consider the position of a parent in a blended family. You have children from your first marriage. Your new spouse has their own children. You sit down with a solicitor to make wills. The solicitor explains your options:
Option A: Leave your share of assets in a life interest trust or IPDI for your spouse, with the capital protected for your children. Your children are guaranteed to inherit regardless of what your spouse does after your death.
Option B: Leave everything outright to your spouse in a mirror will, trusting them to pass it on to all the children. After your death, your spouse can change their will at any time. Your children have no guaranteed inheritance.
Option A is safer. Any competent solicitor would explain this. So why would anyone in a blended family choose Option B?
There is only one rational answer: because there is a deal. The first spouse accepts the risk of Option B only because the second spouse has agreed to honour the arrangement. The mutual inclusion of each other’s children is the bargain – each spouse’s promise to provide for the other’s children is the consideration for the reciprocal promise.
The Detriment of the First to Die
Current law focuses on whether the stepchildren suffered detriment by relying on an expectation of inheritance. But this frames the question incorrectly. The real detriment was suffered by the first spouse to die.
When Reginald McLean chose mirror wills over a protective trust, he gave something up. He surrendered the certainty that his children would inherit. He accepted a risk – the very risk that materialised. He did so in reliance on an understanding with Maureen that the arrangement would be honoured.
This is not mere trust or expectation. This is detrimental reliance in the classic sense recognised by proprietary estoppel. The first-to-die:
- Received an assurance (the mutual mirror will structure)
- Relied on that assurance by forgoing a protective trust
- Suffered detriment – the loss of the opportunity to secure their children’s inheritance
The Supreme Court in Guest v Guest [2022] UKSC 27 confirmed that proprietary estoppel exists to prevent unconscionable conduct. The focus is not merely on compensating detriment, but on holding people to their promises when it would be unconscionable to allow them to resile.
What could be more unconscionable than a surviving spouse receiving an entire estate – the benefit of the mirror will arrangement – and then refusing to honour their side of the bargain?
The Inclusion of Stepchildren IS the Evidence
In non-blended families, mirror wills prove nothing. Spouses naturally want to benefit each other and their shared children. No inference of a binding agreement can be drawn from the structure alone.
But blended families are different. A stepparent owes no legal duty to stepchildren. There is no presumption of natural affection sufficient to explain a testamentary gift. When a stepparent voluntarily includes stepchildren in their will – children who would otherwise have no claim on their estate – that is a positive choice that demands explanation.
The only coherent explanation is reciprocity. Each spouse includes the other’s children because the other spouse is doing the same. The structure itself evidences the bargain.
This is not a radical proposition. It is common sense. Ask anyone making a blended family mirror will why they are including their stepchildren, and they will tell you: because my spouse is including my children. That is a deal. The law should recognise it as such.
A Proposed Test for Blended Family Wills
We propose that in blended family mirror wills, courts should be entitled to infer a mutual arrangement from the testamentary structure itself, rebuttable by evidence to the contrary.
The inference would arise where:
- The testators are in a blended family (one or both have children from previous relationships)
- Both wills include provision for stepchildren (to whom no legal duty is owed)
- The wills are made contemporaneously in materially identical terms
Once the inference arises, the burden shifts. The party seeking to resile from the arrangement must explain why the structure exists if not as a mutual agreement. In the absence of a credible alternative explanation, the court should find that the wills were mutual.
This approach has support in existing doctrine. In Re Basham [1986] 1 WLR 1498, a stepdaughter was awarded her stepfather’s entire estate based on proprietary estoppel. The court recognised that giving up opportunities – forgoing a tied cottage, not moving away – could constitute detrimental reliance. The first-to-die in a blended family mirror will has similarly given up the opportunity to protect their children through a trust structure.
Importantly, Judge Mann in McLean explicitly left the door open: “At least as a matter of principle, it is not easy to see why an estoppel should not operate in the realms of mutual wills if the evidence were clear enough… Mutual wills operates in the realms of equity in order to prevent injustice, and that is what estoppels do as well.”
Our argument provides the principled basis for finding that evidence “clear enough” in blended family cases.
The Time for Reform
The Law Commission’s May 2025 report on Modernising Wills Law signals appetite for change. Among its recommendations is that property subject to mutual wills arrangements should be available for claims under the Inheritance (Provision for Family and Dependants) Act 1975. This recognises that the current framework leaves vulnerable parties exposed.
But legislative reform takes time. In the meantime, courts have the tools to develop the law incrementally. The principles of proprietary estoppel, properly applied to blended family mirror wills, can deliver justice without waiting for Parliament.
What is needed is a test case – the right facts, the right evidence, and the willingness to make the argument.
Conclusion
The current law produces manifest injustice. A spouse can accept the benefit of a mirror will arrangement, inherit their partner’s entire estate, and then disinherit their partner’s children with impunity. This cannot be what equity was designed to permit.
Mirror wills in blended families are different from mirror wills in other contexts. The inclusion of stepchildren – people to whom no duty is owed – can only sensibly be explained as part of a reciprocal arrangement. The law should recognise this reality.
We believe the argument set out in this article could break new ground. If you have been affected by a situation like this, for example – if a stepparent has changed their will after your parent’s death and cut you out of an inheritance you were promised, we would be interested to hear from you.
The right case could change the law for millions of blended families.
This article represents the views of Paul Wood FRSA and is intended to promote discussion of an area of law that we believe requires development. It does not constitute legal advice. If you have a potential claim, please contact us for a confidential discussion of your circumstances.
