Can an adult who has a guardian still make a Will?

A person for whom an adult guardianship or trusteeship order is in place has some difficulty managing his or her own affairs, otherwise there wouldn't be someone appointed to help out. We know that mental capacity is needed to make a valid Will, and the existence of a guardian or trustee suggests that the person's capacity is diminished. Trusteeship orders are not the same as Enduring Powers of Attorney, in the sense that an individual with full capacity can choose to invoke their Power of Attorney for purposes of convenience. That can't happen with a trusteeship order because a lack of capacity must be proven before an order is made.

However, I still believe that it is a mistake to assume, without looking more closely, that this person cannot make a Will.

Firstly, if the order in place is only for guardianship, which involves help for health, medical or personal decisions, that does not suggest in any way that there is impairment of the ability to deal with finances.

Secondly, mental capacity can be a very fluid thing. Keep in mind that I am not a doctor, and that my observations are from a lawyer's perspective in judging whether I believe a person has sufficient capacity to make a Will. As lawyers, our responsibility is to help a person make a Will unless is VERY clear that the person has no ability to do so. Those of us dealing with individuals who mental incapacity is in the early stages know that there are good days and bad days, and even within the good days, some parts of the day are better than others. It's quite possible that the person can still make a Will on one of their good days.

The existence of a trusteeship order itself is not proof that the person doesn't have capacity to make a Will, and it doesn't legally bar the person from making a Will.