Challenging a Will in the UK: Testamentary Capacity and Undue Influence Explained

By: Qarrar Somji

Date: 15/09/2025

For a Will to be valid, the person making it, known as the testator, must have sufficient mental capacity. In addition, they should not have been pressured into making their Will in a certain way, which is known as undue influence

If the testator lacked the necessary mental understanding of their Will, referred to as a lack of testamentary capacity, or they were unduly influenced, their Will is likely to be invalid and could be legally challenged.

What is Testamentary Capacity?

Testamentary capacity is the level of understanding that an individual needs to make a valid Will. Where someone has good days and bad days, for example, if they suffer from dementia, it may be the case that on some days they have sufficient capacity, while on others they do not. If this is the case, their solicitor or a mental health professional should have made notes at the time explaining why they believed the individual was able to make a Will, and a medical assessment in support should have been commissioned. 

The case of Banks v Goodfellow (1870) sets out a legal test for capacity, known as the Banks v Goodfellow test. The case states that the individual making the Will must:

  • Understand the nature and effect of the Will
  • Understand the nature and extent of the estate that they are leaving in the Will
  • Be able to consider any moral claims that may exist to their estate, for example, from a spouse or child

In addition, the Mental Capacity Act 2005 (the Act) sets out a statutory test for determining capacity, as follows:

“a person lacks capacity in relation to a matter if at the material time he is unable to make a decision for himself in relation to the matter because of an impairment of, or a disturbance in the functioning of, the mind or brain”

Making a decision for themselves means that the individual must be able to:

  • Understand information relating to the decision
  • Retain this information
  • Consider the information so that they can make a decision
  • Communicate the decision in some way

Challenging a Will on Testamentary Capacity

If you are considering challenging a Will on testamentary capacity grounds, you will need to establish that the individual did not meet the criteria for mental capacity at the time the Will was signed. 

It will be necessary to put together evidence showing that the testator did not have sufficient understanding. This is not simple or straightforward, and generally requires statements from those around the testator at the time, which could include family, friends, social workers and healthcare professionals, the solicitor’s file from the preparation of the Will, financial records, and expert medical reports.

The first step is generally to speak to an expert contentious probate solicitor. They will be able to advise you on your case and, where necessary, enter a caveat at the Probate Registry to stop a Grant of Probate from being issued while concerns over the validity of the Will exist.

In some cases, your solicitor may be able to negotiate a settlement with the Will’s executors, avoiding the need for court hearings.

Challenges to Wills on the grounds of lack of mental capacity are increasing due to concerns around the understanding of testators with illnesses such as dementia.

What is Undue Influence in Wills?

If a testator is pressured or coerced by an individual into making a Will in that individual’s favour, or in favour of a friend or relative of that individual, and the testator would not otherwise have left their estate in this way, this is undue influence. 

Red flags that could indicate scope for undue influence include:

  • The testator is elderly or vulnerable and depends on one individual for their care
  • The testator has been isolated from friends and family
  • A Will has been substantially changed for no apparent reason, for example, someone has been cut out of the Will
  • A Will is changed at the last minute
  • The new Will contradicts the testator’s earlier stated wishes
  • A new beneficiary is included in the Will
  • A new beneficiary arranged appointments with the solicitor
  • A new Will was not prepared by a solicitor

Challenging a Will for Undue Influence

If you need to know whether you have grounds to challenge a Will on the basis of undue influence, you should speak to a specialist contentious probate solicitor. 

A robust case will need to be established, and this will usually involve obtaining statements from those in the testator’s life at the time, records of any previous Wills, and evidence of the testator’s state of mind.

Evidence to challenge a Will needs to be as comprehensive as possible, showing the way in which the testator’s wishes were overridden.

Solicitors should consider undue influence in Will writing when taking instructions, and their file notes may be helpful in establishing why changes were made.

The court will consider whether the individual in question overwhelmed the testator’s wishes, and look at the circumstances of the case, including issues such as:

  • The testator’s situation, including their age, mental capacity and health
  • The nature and duration of any influence
  • The relationship between the testator and the individual accused of unduly influencing them
  • The timing of any changes made to a Will
  • How reasonable the Will is, in the light of the testator’s relationships and circumstances

If the court believes that the influence was more than just persuasion, and that the testator would not have left their estate in the way that they did but for the undue influence, the court may decide that the Will is invalid.

How Long to Contest a Will?

There is no time limit for contesting a Will on the grounds of testamentary capacity or undue influence; however, you are strongly recommended to take action as soon as possible if you believe you have a case.

Once a Grant of Probate is issued and the estate administration begins, there is a risk that the executors could decide to distribute funds.

In addition, the sooner you can start your case, the fresher everything will be in people’s memories, and the easier it will be to gather evidence.

If you are considering contesting a Will for lack of testamentary capacity or undue influence, speak to us today.

Contact Our Wills and Probate Solicitors

If you are considering contesting a Will in the UK and you need advice on the strength of your case, we will be happy to advise you. We can give you guidance on how to contest a Will in the UK and discuss the first steps to be taken.

For information on Wills disputes in the UK and our related services, see our Wills, trusts and probate page.

To speak to one of our expert Wills solicitors, ring us on 0330 173 3980, email us at info@witansolicitors.co.uk or fill in our contact form, and we will talk through your situation with you and discuss how we can assist.

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