Millions of couples could be unknowingly putting their loved ones’ inheritance at risk due to a little-known flaw in the UK’s most popular type of will, a law firm has warned.
The issue centres on so-called ‘mirror wills’. Simple to set-up, this type of will is commonly used by married couples and civil partners to ensure when one partner dies everything from property to ISAs and savings accounts goes to the survivor.
When they later pass away, the estate, after inheritance tax, is typically assumed to go to the children and potentially grandchildren.
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But lawyers are warning that there's a catch which may fail to protect first families if circumstances change after death and it could lead to more inheritance disputes. This is because once the first partner has died, the survivor is free to rewrite their will at any time.
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In addition, any remarriage automatically cancels the previous will.
The result can mean children named in the original will can be quietly pushed out of the inheritance altogether.
Simarjot Singh Judge, founding partner of law firm Judge Law, said the consequences can be devastating and often come as a complete shock.
“While many people assume their estate will automatically stay ‘in the family’, the reality can be very different if a surviving partner remarries, separates or later changes their will,” he said.
"People are stunned when they discover having a will doesn't necessarily mean their children or grandchildren will inherit. In many cases, assets can legally pass to a new spouse, their family, or even be swallowed up by care costs – despite what the original intentions were," Judge added.
He said this loophole can also affect grandchildren in unexpected ways.
He said: "If your child inherits from you and later dies, their spouse may receive everything. If that spouse then remarries, your estate could end up benefiting an entirely different family – potentially someone else's grandchildren and not your own."
How mirror wills work
Mirror wills are often mistaken for a binding agreement, but in law they are simply two separate wills.
"Either partner can change their will at any time, without consent or notification, meaning the original arrangement relies entirely on trust rather than legal protection,” said Judge.
The main risk arises after the first death. Typically, everything passes to the surviving partner who then has full freedom to rewrite their will.
"They can redirect assets to a new partner, favour certain beneficiaries, or exclude children altogether, bringing the original shared plan to an end,” Judge said.
"This frequently causes shock and disputes as children discover their expected inheritance is not guaranteed, even though the survivor’s actions may be legally valid,” he added.
Ways to protect your legacy
To avoid their loved ones losing out, couples may want to consider alternatives to mirror wills that legally protect their bloodline from being disinherited.
"Trust-based wills can offer strong protection by placing assets into a life interest trust. This allows the surviving partner to live in the property or receive income, while preventing them from redirecting the capital away from agreed beneficiaries such as children,” said Judge.
This approach is commonly used in second marriages and blended families.
Judge added: "Mutual wills can also provide protection because they may prevent changes after the first death, but they are complex and interpreted very strictly by the courts. Poor drafting can make them unenforceable so specialist legal advice is essential.”
Families may also reduce risk by ring-fencing certain assets, such as leaving a share of property or investments directly to children while allowing the survivor only use or income.
"Regularly reviewing wills and clearly communicating intentions can further help avoid disputes, as mirror wills offer simplicity rather than guaranteed protection," Judge said.
He added: "You don't need a title or a fortune to want certainty that what you've worked for will support your children and grandchildren, not disappear due to a technicality.
"It's important that families review existing wills, especially if they were drafted years ago, to ensure their wishes will still be honoured in the future."
