What Makes a Will Invalid in the UK: Every Ground Explained

The Legal Requirements for a Valid Will

The foundation of every valid will in England and Wales is section 9 of the Wills Act 1837. The section sets out four cumulative requirements, all of which must be met. If any one of them is missing, the will is not valid as a matter of law.

1. The will must be in writing (any legible medium, including handwriting).
2. It must be signed by the testator, or by some other person in the testator’s presence and by their direction.
3. The testator must make or acknowledge the signature in the presence of two or more witnesses present at the same time.
4. Each witness must attest and sign the will, or acknowledge their own signature, in the testator’s presence.

All four elements are mandatory. A will signed in the presence of only one witness, or where one witness signed on a different occasion from the other, does not satisfy s9 and is entirely void. There are no exceptions and no judicial power to cure the defect.

Lack of Testamentary Capacity

To make a valid will, the testator must have been of “sound mind, memory and understanding” at the moment of execution. The legal test derives from Banks v Goodfellow [1870] LR 5 QB 549, where Cockburn CJ set out four criteria that must all be satisfied:

1. The testator must understand the nature of making a will and its effects — that is, they are creating a document that will distribute their property on death.
2. They must understand the extent of the property they are disposing of — a broad, not precise, understanding of the estate is required.
3. They must understand the claims of those who might reasonably expect to benefit, even if those persons are ultimately excluded from the will.
4. They must not be suffering from any disorder of the mind that poisons the affections, perverts the sense of right, or prevents the exercise of their natural faculties in disposing of their property.

A person can have capacity even with dementia, if the condition was not sufficiently advanced at the time of signing to satisfy criterion 4. Equally, a person with advanced cognitive decline may have had a “lucid interval” during which a valid will could be made. What matters is the position at the date of execution, not the general state of the testator’s health.

A duly executed will raises a rebuttable presumption of capacity. The challenger must bring evidence sufficient to raise a real doubt, whereupon the burden shifts to the propounder of the will to prove on the balance of probabilities that the testator had capacity. Medical records, contemporaneous letters, witness statements from those who knew the testator, and retrospective consultant psychiatrist assessments are all commonly used as evidence.

Lack of Knowledge and Approval

Even where a testator had capacity, the will can be challenged on the ground that they did not know and approve its contents. The testator must have had an understanding of what the will said and must have freely assented to it at the time of execution.

Knowledge and approval are presumed where the will has been duly executed by a testator with capacity. However, this presumption is displaced where suspicious circumstances surround the preparation or execution of the will. Classic indicators include:

• A beneficiary who stands to gain substantially was involved in drafting or procuring the will.
• The testator was blind, illiterate, or did not speak the language in which the will was written and the will was not read aloud to them.
• A frail testator made a sudden, dramatic change to long-standing testamentary plans in the period immediately before death.
• The will was not read over by the testator before signing, or the testator’s physical or mental state meant they could not have absorbed the contents.

Where suspicious circumstances are established, the court requires affirmative proof — beyond mere execution — that the testator actually understood and approved each provision. The leading authority is Barry v Butlin [1838]; the modern approach is set out in Gill v Woodall [2010] EWCA Civ 1430, where the Court of Appeal emphasised that the test is not purely objective: the court must look at all the circumstances, including what the testator did and said at the time of execution.

Undue Influence

Undue influence requires something more than persuasion, nagging, emotional appeals, or the use of affection. The pressure must amount to coercion that overpowers the free agency of the testator so that the will that results is not truly the testator’s own. As Sir James Hannen stated in Hall v Hall [1868]:

“Persuasion is not unlawful, but pressure of whatever character, whether acting on the fears or the hopes, if so exerted as to overpower the volition without convincing the judgment, is a species of restraint under which no valid will can be made.”

Unlike undue influence in a contract claim, there is no presumption of undue influence in will challenges — even in relationships of great dependence or trust. The challenger must prove it on the balance of probabilities, usually through circumstantial evidence, because direct evidence of coercion is rarely available. Courts look at:

• Whether the testator was isolated from family or other advisers by the person who benefits.
• Dependency arising from age, illness, or financial reliance on the influencer.
• Late-life changes in the will that favour a carer, cohabitant, or new acquaintance.
• Exclusion of long-standing beneficiaries without any apparent reason.
• Whether the testator had independent legal advice when making the will.

It is worth distinguishing undue influence from proprietary estoppel. Where someone has been promised an inheritance and has relied on that promise to their detriment, they may pursue an estoppel claim against the estate even if the will is otherwise valid. Estoppel does not challenge validity; it may confer rights despite a valid will making no provision.

Fraud and Forgery

A will is void — not merely voidable — where it was procured by fraud or where it is a forgery. There are two distinct scenarios:

• Fraud: The testator was deceived about the nature of the document they were signing (e.g. told it was a power of attorney rather than a will), or deceived about the identity or circumstances of a beneficiary. Because the consent of the testator was obtained by deception, the will cannot be given effect.
• Forgery: The signature on the will is not that of the testator, or was placed there without their authority. A forged will has never been executed and is a nullity. Forgery is also a criminal offence under the Forgery and Counterfeiting Act 1981.

Fraud and forgery claims require strong evidence — usually handwriting expert analysis, witness statements, financial records, or CCTV/digital evidence. The standard of proof remains the civil balance of probabilities, but courts require cogent evidence commensurate with the seriousness of the allegation (Re B [2009] 1 AC 11).

Improper Execution

Many wills — particularly DIY and homemade wills — fail not because of any dishonesty or incapacity, but simply because the execution formalities under s9 of the Wills Act 1837 were not followed correctly. The most common execution failures are:

Alterations made after a will has been executed are governed by s21 of the Wills Act 1837. A crossing-out, addition, or interlineation is void unless it is itself executed with the same formalities as the will (signed by the testator and witnessed by two witnesses near the alteration). This means that writing amendments into the margin of a signed will without re-witnessing them simply restores the original wording — the alteration is treated as never having been made.

If you need to change your will, the only safe routes are to execute a new will containing a revocation clause, or to execute a codicil — a separate document that amends specific provisions and is itself signed and witnessed with full s9 formalities.

Revocation

A validly executed will can be rendered of no effect by revocation. The principal methods are set out in the Wills Act 1837 and subsequent case law:

Revocation by marriage

Under s18 of the Wills Act 1837, marriage automatically revokes any existing will. This is one of the most frequently overlooked grounds for invalidity. Many people make a will, then marry years later, unaware that their existing will is no longer valid.

The only exception is where the will was made in express contemplation of marriage to a specific person. A general “contemplation of marriage” clause naming no one is insufficient. The will must recite something such as “I make this will in contemplation of my forthcoming marriage to [full name].” If the named marriage does not then take place, the will is not revoked by a subsequent different marriage.

Effect of divorce

Divorce does not revoke a will. However, under s18A of the Wills Act 1837 (as inserted by the Law Reform (Succession) Act 1995), on the dissolution or annulment of the testator’s marriage or civil partnership:

• Any appointment of the former spouse as executor lapses.
• Any gift to the former spouse in the will fails and passes as if the former spouse had died on the date of the divorce or annulment.
• The rest of the will remains fully valid.

This means that if you want your former spouse to benefit under your will following a divorce, you must execute a new will expressly confirming the gift. Relying on s18A to “delete” an unwanted former spouse automatically is not the same as making fresh provision for new beneficiaries.

Revocation by a later will

A will is revoked by a subsequent valid will that contains an express revocation clause, which most professionally drafted wills do (“I revoke all former wills and testamentary dispositions previously made by me”). A later will without a revocation clause does not necessarily revoke the earlier one — the two are read together and the earlier will only fails to the extent of any inconsistency.

Revocation by destruction

A testator can revoke a will by burning, tearing, or otherwise destroying it with the intention to revoke it. The destruction must be of the will itself (not merely a copy) and must be accompanied by the requisite intention. Accidental destruction does not revoke a will, and courts have reconstructed accidentally destroyed wills from secondary evidence.

Frequently Asked Questions