Mental health and contesting a will
One of the most common reasons for challenging a Will in England and Wales is when there are doubts about whether the person who made it — known as the testator — had the mental capacity to understand what they were doing.
Mental health and ageing are increasingly significant factors in will disputes. It is estimated that 1 in 4 British adults experiences a diagnosable mental health problem in any given year, and around one in six experiences one at any time. With conditions such as dementia, Alzheimer’s disease, depression, bipolar disorder and delusional disorders becoming more prevalent, questions of mental capacity at the time of making a will are now more frequent than ever
If there are concerns that the deceased was not of sound mind when they made their will, it may be possible to contest the will and seek to have it declared invalid.
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What Does “Lack of Mental Capacity” Mean in Law?
Under English law, a will can only be valid if the person making it understands:
- The nature of the act and its effects – that they are making a will, and that it will distribute their estate after death.
- The extent of the property being disposed of – they do not need to know the exact value, but must have a general awareness of what they own.
- The claims to which they ought to give effect – they must be able to comprehend and appreciate the people who might expect to benefit (such as close family members).
- That no disorder of the mind influences their decisions – the will must not be the product of delusion, coercion, or mental illness.
These principles were established in the leading case of Banks v Goodfellow (1870), which remains the cornerstone of modern will-making law. If any of these elements are missing, the will may be invalid due to lack of testamentary capacity.
Common Mental Health Conditions That Can Affect a Will
Certain conditions are more likely to give rise to concerns about capacity:
- Dementia and Alzheimer’s disease – often progressive, these can impair memory, reasoning and judgment.
- Schizophrenia or psychosis – may cause delusions or distorted perceptions of reality, influencing testamentary decisions.
- Bipolar disorder and severe depression – during manic or depressive episodes, decision-making can be impaired.
- Brain injuries or strokes – may affect cognitive functioning, especially in older testators.
- Substance abuse – alcohol or drug dependency may impair awareness and reasoning.
However, having a mental illness does not automatically mean someone lacks capacity. Capacity is task-specific and time-specific — a person may have lucid intervals or retain sufficient understanding to make a valid will, even if they are generally unwell.
How Capacity Is Assessed
When a solicitor or will-writer suspects that a client may have diminished mental capacity, they should follow what is known as the “Golden Rule” (from Kenward v Adams [1975]). This advises that:
- The solicitor should ensure the testator’s capacity is assessed by a medical professional, ideally a doctor experienced in capacity assessments.
- The doctor should witness or confirm the will-making process and provide a written statement confirming the testator’s understanding.
- This evidence can later help defend the will if its validity is challenged.
If the Golden Rule is not followed and doubts arise after death, it becomes easier for disappointed beneficiaries to allege lack of capacity.
Lacking Mental capacity is ground for Challenging a Will – a case study
One of the most famous cases of disputed wills in the UK, due to mental health problems, was the Kostic family.
In 2005, pharmaceuticals mogul Branislav Kostic died leaving all his £8.3 million fortune to the Conservatives party. At this point, his son Zoran had to contest the Will at the High Court, arguing that his father was ‘deluded and insane’ when he wrote his Will in the 1980s. Apparently, he wrote it after saying Mrs Thatcher would save the world from ‘satanic monsters’. His son claimed that the whole of the estate to the party was ‘in part the product of the state of his mind’.
The story of Branislav Kostic states that in 1984 he became mentally ill and diagnosed as suffering from paranoia. His son said that he was tormented by delusions that other members of the family were part of a worldwide conspiracy of terrorists and criminals who were trying to kill him. Due to this, Clare Montgomery QC – representing Mr Kostic’s son – said the Conservatives ‘only benefited because the testator became mentally ill’. She argued that these delusions influenced Mr Kostic’s decision to leave his entire estate to the political party. The High Court agreed, concluding that the will was indeed the product of mental illness.
This is an extreme, but real, case of how mental disorder can fundamentally invalidate a will, particularly when the terms of the will are so unusual that they appear to reflect delusional thinking,
justifying an inheritance claim after someone with a mental disorders dies. Solicitors and lawyers, who will act discreetly, can help to solve things quickly and, if possible, avoiding Court.
Evidence Used to Challenge a Will for Lack of Capacity
When bringing a claim, making sure that you have the right evidence is crucial. Common sources include:
- Medical records – GP notes, hospital records, psychiatric reports, or memory clinic assessments.
- Witness statements – from family members, carers, or friends who can describe the deceased’s mental state.
- Solicitor or will-writer notes – recording observations about the testator’s understanding or unusual behaviour.
- Expert reports – retrospective capacity assessments prepared by medical experts after reviewing the evidence.
Courts will examine this evidence carefully to determine whether, on the balance of probabilities, the testator lacked testamentary capacity at the time the will was made.
Other Grounds for Contesting a Will
Although lack of capacity is one of the most common grounds, others may include:
- Undue influence – where someone has pressured or coerced the testator.
- Lack of knowledge and approval – where the testator did not fully understand or approve the contents.
- Fraud or forgery – where the will was not genuine.
- Failure to comply with legal formalities – such as improper witnessing.
Sometimes multiple grounds overlap; for example, an elderly testator with dementia may also be more vulnerable to undue influence.
How to Contest a Will for Lack of Mental Capacity
If you believe a will was made without proper mental capacity, the following steps are typical:
- Get hold of a copy of the will and the grant of probate, if issued.
- Seek early legal advice from a solicitor experienced in contentious probate.
- Your solicitor may enter a caveat at the Probate Registry to prevent probate being granted while the dispute is investigated. (A probate caveat is a formal notice filed at a Probate Registry to temporarily prevent a Grant of Probate from being issued)
- Gather medical and factual evidence to support the claim.
- Engage in pre-action correspondence – sometimes the dispute can be resolved before going to court.
If no resolution is reached, a claim is issued in the High Court (Chancery Division) for the will’s validity to be determined.
Many cases settle without trial, particularly through mediation or negotiation between the parties.
Challenging a Will Contest How Much Time Do I Have?
There are strict limits for making an Inheritance Act claim. If you are bringing a claim under the Inheritance (Provision for Family and Dependants) Act 1975, you normally have six months from the date of the Grant of Probate to issue proceedings to contest a will, or you risk losing your right to claim entirely. In very limited situations, court may permit a claim after this period – but general terms, you should stick to that six month deadline.
Claims about the validity of the will itself (for example, for lack of capacity or undue influence) technically do not have a fixed limitation period, but delay can make the case harder — especially once the estate has been distributed. For that reason, you should act quickly and take advice as soon as concerns arise.
So, if you think you might have grounds for a claim it is vital that you speak to a specialist solicitor ASAP.
How the Courts Decide
- Courts will consider all the evidence “in the round”.
- They typically start with a presumption of capacity — that a person making a will is presumed to have the mental capacity to do so unless proven otherwise.
- The burden of proof shifts depending on the evidence:
- The party alleging lack of capacity must produce sufficient evidence to raise a genuine doubt.
- Once raised, the burden falls on those propounding the will (usually the executors or beneficiaries) to prove capacity.
Courts also consider consistency. If earlier or later wills show a logical pattern of distribution, and the disputed will is radically different, that can support an argument that the testator’s mind was affected by illness or delusion at that time.
Practical Signs a Will May Be Invalid
You may wish to seek advice if you notice any of the following:
- The deceased had a diagnosed mental illness or dementia around the time the will was made.
- The new will is radically different from previous versions.
- The will benefits someone unexpected or excludes close family without reason.
- The solicitor or witnesses noticed confusion, paranoia or forgetfulness.
- There is no medical evidence confirming capacity, despite concerns.
These may all suggest that the will could be challenged.
The Role of Solicitors in Mental Capacity Disputes
Contentious probate solicitors play a vital role in investigating such cases. They will:
- Review medical and legal documentation.
- identify and instruct independent medical experts.
- Attempt to resolve disputes through correspondence or mediation.
- Represent clients in the High Court if litigation becomes necessary.
Experienced lawyers will act discreetly and sensitively, as these disputes often arise within families already grieving a loved one.
Avoiding Will Disputes: Tips for Testators
For anyone concerned about future challenges, it helps to:
- Make the will while clearly of sound mind, ideally with medical confirmation if there is any doubt.
- Use an experienced solicitor, not a DIY will template. and watch out for will writers. While some are perfect incompetent, the majority are unqualified and unregulated with limited training and may not even be insured in case something goes wrong– they are certainly very unlikely to carry the huge level of indemnity insurance that solicitors are forced to cover
- Explain reasons for decisions in a signed letter of wishes (particularly if excluding close relatives).
- Ensure proper witnessing and storage of the will.
- Review the will regularly as circumstances or health change.
- Taking these precautions can greatly reduce the risk of disputes later.
Real-World Context: The Rise in Capacity-Related Disputes
With an ageing population and increasing rates of dementia, will disputes involving mental capacity have grown significantly. The Ministry of Justice and The Law Society have both noted a steady rise in contentious probate cases reaching the High Court in recent years.
According to Alzheimer’s Research UK, over 1 million people in the UK are expected to be living with dementia by 2030. This means many families will face complex questions about whether their loved one was capable of making valid testamentary decisions.
What happens if all the beneficiaries agree with changes to how the estate is distributed under the will?
If everyone entitled under the will (or under intestacy if no valid will exists) agrees, they can vary the distribution of the estate using a Deed of Variation. This allows beneficiaries to redirect their entitlement — for example, to include someone left out — without challenging the will itself.
To learn more, see our page: – Can a Will Be Changed After Death?
Why Specialist Advice Matters
Claims involving mental capacity are legally and medically complex. Early advice from an experienced contentious probate solicitor can make all the difference. At Bonallack & Bishop, our team regularly helps clients across England and Wales contest wills on grounds including lack of capacity, undue influence and lack of knowledge or approval.
We can review your case confidentially, assess the available evidence, and advise on the best way forward — whether through negotiation or court action
If you are worried about someone in your family who might not be able to write a proper Will for mental health reasons, it might be a good idea to do some research and get specialist legal advice before you and your family have to go through probate solicitors, disputes and Courts after the funeral. After all, those are the least things you should worry about when someone dies.
Click here to read more about questions regarding mental capacity for wills
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