For the Will to be valid, the person making the Will must have knowledge of, and approve, its contents. You can challenge a Will on the basis of lack of knowledge – even if the Will appears to be executed properly, and even if you know the testator was of sound mind. You would need to provide evidence that suggested the testator was not aware of the contents of the Will, or that there were some suspicious circumstances.
Prior to the decision in Gill v Woodall , where the Testator (the person who made the Will) had testamentary capacity, a two-stage test was applied to determine if they had ‘knowledge and approval’ of the contents of the Will (Barry v Butlin). The two stage test involved consideration of:
The ‘propounder’ of the Will is the person presenting the Will and arguing that it should stand. So the Court had to consider whether any evidence brought forward by the propounder put to rest the suspicions of the court.
However, in Gill v Woodall , the Court questioned this approach, where a judge had heard evidence of fact and expert opinion over many days relating to the Deceased and to the execution of the Will. Where this was the case, the Court of Appeal held that the Court should consider all relevant evidence that was available to them and draw such inferences as it could from all of the material available taken together, enabling them to reach a conclusion as to whether or not the burden of establishing knowledge and approval of the contents of the document had been discharged. This is a single-stage test.
This was revisited in Sharp v Hutchins  in which the Judge was satisfied that the single-stage test proposed in Gill was the correct approach – but that the Court could use the two-stage test to cross check the conclusions that were reached using the single stage test.
Going forward, the single stage test is the relevant test that will be applied in determining whether the Testator had knowledge and approval of the contents of the Will – but the two stage test can be applied as a cross check.
Although Wills do need to meet quite a number of requirements by law (see: Lack of valid execution) it is perhaps surprising how little formality is required for such an important document. Anyone can prepare a Will – regardless of whether they are legally trained or not. The Will does not have to be typed or even in the testator’s handwriting. It does not even need to be signed by the testator as it can be signed on his behalf. Neither does it need to be signed in front of witnesses – the signature can instead be acknowledged. The witnesses to a Will do not need to know the testator or have knowledge of the contents of the Will. Neither do they need to be people who might survive the testator so if there is ever a question over validity, it is possible the witnesses would not be available to give evidence. Lastly, there is no requirement that someone be informed when a new Will is executed – this can be done entirely in secret. Consequently if a testator makes a suspicious Will, there is every possibility that his family will not discover the fact until after his death, when it is too late to speak to him about the contents or assess his mental state.
Given all of the above, it is perhaps not surprising that Wills do appear where the testator is held not to have full knowledge and approval of the contents. Vulnerable testators can be duped into making a Will which they believe gifts their property to their choice of beneficiaries where in reality, it does not. Where circumstances appear to be suspicious, it may be possible to bring a claim. An example might be if the Will contained a significant gift to someone who helped to prepare it.