A dementia diagnosis does not automatically prevent someone from making an LPA. The important question is whether they still have the mental capacity to understand the document and the authority they are giving to their attorneys.
Mental capacity is decision-specific and may fluctuate. A person may therefore be able to make an LPA during the earlier stages of dementia if they understand its purpose, the powers being granted and the possible consequences.
A certificate provider must confirm that the person understands the LPA and is not being pressured into making it.
If the person has already lost the capacity required to create an LPA, it is too late to make one. A family member or other suitable person may instead need to apply to the Court of Protection to become a deputy. That process is generally more involved and can be more expensive than arranging an LPA in advance.