Inability to make decisions
5.—(1)  For the purposes of section 4, a person is unable to make a decision for himself if he is unable —
(a)to understand the information relevant to the decision;
(b)to retain that information;
(c)to use or weigh that information as part of the process of making the decision; or
(d)to communicate his decision (whether by talking, using sign language or any other means).
(2)  A person is not to be regarded as unable to understand the information relevant to a decision if he is able to understand an explanation of it given to him in a way that is appropriate to his circumstances (using simple language, visual aids or any other means).
(3)  The fact that a person is able to retain the information relevant to a decision for a short period only does not prevent him from being regarded as able to make the decision.
(4)  The information relevant to a decision includes information about the reasonably foreseeable consequences of —
(a)deciding one way or another; or
(b)failing to make the decision.
[UK MCA 2005, s. 3]