What is the Difference Between Dementia and Eccentricity? Where the UK Courts Draw the Line in 2026

The difference between Dementia and Eccentricity: In 2026, UK courts distinguish between Dementia (a clinical impairment of the mind) and Eccentricity (a lifestyle choice or personality trait). Under the Banks v Goodfellow test, a person can be eccentric, hold “strange” beliefs, or even be unkind to their family, and still have the legal capacity to make a Will. However, if an eccentricity is actually a “delusion” caused by a cognitive disorder that poisons the testator’s affections, the line is crossed. The 2026 courts focus on functional ability: did the “quirk” prevent the person from understanding their choices, or was it simply an exercise of their free will?

Read our complete guide on contesting a will for lack of capacity.

The Freedom to be “Difficult”

In English law, the “freedom of testation” is a sacred principle. It means that, unlike in some other European jurisdictions, you have the right to be as unfair, unkind, or unusual as you wish with your own money. However, as we move through 2026, the rise in cognitive disorders has made the boundary between a “difficult personality” and a “diseased mind” increasingly thin.

At Contest A Will Today, we specialize in identifying exactly where that line was crossed to ensure that a Will reflects a person’s true wishes, not their illness.

The “Right to be Quixotic”

The English legal system has long protected the right of an individual to be eccentric. In 2026, the courts remain firm: you do not have to be “fair” or “normal” to make a valid Will. A testator can choose to leave their entire estate to a cat sanctuary while disinheriting their children simply because they prefer animals. This is eccentricity, and it is legally protected.

• The Personality Anchor: If the testator was always eccentric—the “family rebel” or the “hermit”—the court is likely to view an unusual Will as a continuation of their character.
• The 2026 View: Judges now distinguish between eccentricity (a lifestyle choice) and incapacity (a loss of cognitive function). If you’ve always been quirky, your Will can be quirky too.

When Quirkiness Becomes a “Delusion”

The legal line is drawn at the concept of a “testamentary delusion.” A delusion isn’t just a mistake; it is a fixed, false belief caused by a diseased mind.

• Eccentricity: “I am leaving my money to the local park because my children never visit me” (even if the children feel they visit enough).
• Dementia/Delusion: “I am disinheriting my children because I believe they have been replaced by aliens who are poisoning my food” (where this belief is a product of cognitive decline).

In 2026, the courts apply a three-part test for delusions:

1. The Belief is False: The idea has no basis in reality.
2. The Belief is Fixed: The testator cannot be reasoned out of it.
3. The Nexus: The delusion must directly influence the Will. If I believe the moon is made of cheese but I leave my money to my children fairly, the Will stands. If I believe my children are stealing my thoughts and disinherit them because of it, the Will is void.

2026 Case Law: The Shift Toward “Functionalism”

Recent cases in 2026 have emphasized the Functional Test. The court asks: At the moment the pen hit the paper, did the testator have the “mental energy” to understand the claims of those they were disinheriting?

Even if someone is eccentric, the court will check if they could:

• Understand the extent of their property (what they own).
• Appreciate the claims of their family (who they should consider).
• Synthesize this information without being clouded by a disorder.

The 2026 Functional Test

In 2026, judges use a more nuanced approach than previous decades. They look at whether the testator’s personality changed abruptly. A lifelong “grumpy” person disinheriting a relative is seen as consistency. A lifelong “kind” person suddenly becoming paranoid and hostile is often flagged as clinical impairment.

The “Poisoned Affections” Rule

A key strategy in 2026 Will contests is proving that dementia “poisoned the affections” of the testator. If we can show that a medical condition (like Alzheimer’s) created a false sense of resentment toward a beneficiary who was previously loved, the court can strike down the Will, even if the testator appeared “sharp” in other areas of life.

The “Golden Rule” and the Solicitor’s Role

In 2026, the “Golden Rule” is more relevant than ever. This rule suggests that when a solicitor drafts a Will for an elderly or ill person, they should have a medical practitioner witness it or certify capacity.

If a solicitor ignored the testator’s clear eccentricities (e.g., the testator wearing a winter coat in a heatwave or making incoherent statements) and failed to call a doctor, this constitutes a procedural failure. We use these failures to challenge the Will’s validity and, in some cases, pursue professional negligence claims against the drafting firm.

Read our full guide on the Golden Rule here.

Disentangling “Unwise Decisions” from Lack of Capacity

The Mental Capacity Act 2005 (which still forms the backbone of 2026 law) states that a person is not to be treated as lacking capacity merely because they make an unwise decision.

A testator who gambles away their inheritance or leaves it to a controversial cult is making an “unwise decision.” However, our forensic team uses medical audits to show that what appears to be a choice was actually a lack of executive function—an inability to perceive the consequences of the act.

Digital Evidence: The 2026 “Social Footprint”

For the first time, courts are heavily using digital “breadcrumbs” to distinguish eccentricity from dementia.

• Consistency Check: We analyze years of emails and texts. A sudden decline in vocabulary, a shift into aggressive “all-caps” messaging, or repetitive questioning can prove that “eccentricity” was actually the onset of cognitive decline.
• The “Vibe” Shift: A forensic psychiatrist can look at this data to determine if the testator’s “voice” changed, indicating they were no longer the person who wrote their previous, more balanced Wills.

Let’s Do This Together

Contesting a will could become an overwhelming experience if not accompanied by expert guidance and support. Our mission is to provide you with all the needed information, support, and authority to get through this journey, with only one goal in mind: Fairness.

To our team, this process is not about winning; it’s about claiming what was yours from the beginning.

Get your free, no-obligation case assessment. Call 08002980029 or visit contestawilltoday.com

FAQs

1. If my relative was always “difficult” or had strange hobbies, does that make it harder to contest their Will?

Yes, it can. In the UK legal system, consistency is often equated with capacity. If a person has a lifelong history of being eccentric, stubborn, or holding unconventional views, the court may see a “strange” Will as a reflection of their true personality rather than a lack of mental capacity.

To win a challenge, we must prove there was a radical shift in their behavior or that their quirks transitioned into clinical testamentary delusions that specifically poisoned their view of the beneficiaries.

2. Can I challenge a Will if the testator was making “unwise” financial decisions before they died?

Under the Mental Capacity Act 2005, a person cannot be treated as lacking capacity simply because they make a decision that others see as “unwise” or risky. However, in a 2026 legal context, we look for a loss of executive function. If the “unwise” decision was caused by an inability to understand the consequences or a failure to “weigh up” the extent of their estate (often seen in the early stages of dementia), it becomes a strong ground for a claim of lack of testamentary capacity.

3. What is the “Poisoned Affections” rule, and how is it proven?

This rule applies when a medical condition, such as dementia, causes a testator to develop a deep-seated, irrational resentment or paranoia toward someone they previously loved. To prove this in 2026, we use a Medical Audit of GP records and Digital Sentiment Analysis of emails or texts. If we can show that the testator disinherited a child based on a “fixed, false belief” (a delusion) created by their illness, the court can strike down the Will as being “poisoned” by the disease.