In the recent case of Ball & Ors v Ball & Ors  EWCH 1750 (Ch) three of eleven children lost their challenge to the will of their late mother on the ground of lack of testamentary capacity. They claimed her will was invalid on this ground because their mother excluded them from her will in light of a mistaken belief about past events.
The history of the matter is as follows: In 1991, the three claimants reported their father to the police for sexually abusing them when they were younger. Their father, the deceased's husband, pleaded guilty to some of the allegations and was prosecuted. Their mother, upset by her children's actions, subsequently made a will in May 1992 in which she excluded the claimants from benefit, dividing her estate between her eight remaining children and a grandson.
The claimants challenged the will on the basis that the deceased's mistaken belief that the claimants had invented or exaggerated the claims of abuse amounted to a lack of testamentary capacity. They claimed that "[her] mental state was impaired in the sense that she was misled as to crucial facts by [her husband], and she would not have reached those conclusions had she not been misled. Her state of mind was such that her capacity was lacking, because of the serious misapprehension under which she was labouring."
His Honour Judge Matthews held that "I find that, at the time of making her will in May 1992, the testatrix knew that three of her children (now the claimants) had in 1991 complained to the police of sexual abuse of them by her husband in earlier years, and that he had admitted some of this to the police, but not all of it. … Her husband was convicted on his own guilty pleas of some of the charges … I do not accept that he misled the testatrix… on the evidence I am satisfied that at the time of making her will she was not labouring under any significant mistake at all as to the guilt of her husband."
For a will to be valid, the testator must have sufficient mental capacity. The test for capacity to execute a valid will was established in the case of Banks v Goodfellow  LR 5 QB 549. A testator must:
- Understand the nature of making a will and its effects
- Understand the extent of the property of which they are disposing
- Be able to comprehend and appreciate the claims to which they ought to give effect
- Have no disorder of the mind that perverts their sense of right or prevents the exercise of their natural faculties in disposing of their property by will.
A mistaken belief does not itself operate to invalidate a will. What it may do, however, is provide a basis upon which to say that the testator was either suffering from an "insane delusion" or did not possess a sufficiently sound memory for the purposes of making a will, and as such did not have the requisite testamentary capacity to execute a will.
In the case of Re Bellis  141 LT 245, the deceased made a will shortly before her death in which one of her two daughters benefited more greatly than the other. This was because the deceased thought she had been financially assisting the other daughter, so wanted to put them on an equal footing. She was however mistaken in her belief as to what financial provision she had already provided, and had now favoured one daughter considerably more than the other.
In that case, the Judge said that "[The question] is not whether the will is avoided by a mistake of fact. Mere mistake of fact as to persons or property would not stand in the way of probate..." The Judge went on to say that the question to be asked is "was [the mistaken belief] an insane delusion upon which her testamentary action … proceeded or an illusory belief of such a character as, having regard to the facts of the case must be held to displace the prima facie proofs of testamentary capacity?" In this case, the Judge found that the testatrix was suffering from an illusory belief and as such, lacked the requisite capacity to make a valid will.
Therefore, although it may be apparent that the deceased was under a mistaken belief, a mere mistake is not enough. It must be proved that that false belief resulted from a mental incapacity.
There is an alternative option to challenge the will that was not pursued in the case of Ball & Ors. That is relying on the principle of "fraudulent calumny". This is where a mistaken belief has come about because of a false representation made to the testator for the purpose of persuading the testator to exclude an individual from a benefit in his/her will. As the Courts have said "… if A poisons the testator's mind against B, who would otherwise be a natural beneficiary of the testator's bounty, by casting dishonest aspersions on his character, then the will is liable to be set aside." Although this may appear to be an option, potential claimants need to be aware that fraudulent calumny is an extreme form of undue influence that is often not easy to prove.