s 4 Persons who lack capacity
4.—(1) For the purposes of this Act, a person lacks capacity in relation to a matter if at the material time the person is unable to make a decision for himself or herself in relation to the matter because of an impairment of, or a disturbance in the functioning of, the mind or brain. (2) It does not matter whether the impairment or disturbance is permanent or temporary. (3) A lack of capacity cannot be established merely by reference to —(a) a person’s age or appearance; or (b) a condition of the person, or an aspect of the person’s behaviour, which might lead others to make unjustified assumptions about the person’s capacity. (4) In proceedings under this Act (other than proceedings for offences under this Act), any question whether a person lacks capacity within the meaning of this Act must be decided on the balance of probabilities. (5) Subject to section 21, no power which a person (“D”) may exercise under this Act —(a) in relation to a person who lacks capacity; or (b) where D reasonably thinks that a person lacks capacity, is exercisable in relation to a person below 21 years of age.