(1) The trustees may not authorise a person to exercise any of their asset management functions as their agent except by an agreement which is in or evidenced in writing.

(2) The trustees may not authorise a person to exercise any of their asset management functions as their agent unless -

(a) they have prepared a statement that gives guidance as to how the functions should be exercised ("a policy statement"), and

(b) the agreement under which the agent is to act includes a term to the effect that he will secure compliance with -

(i) the policy statement, or

(ii) if the policy statement is revised or replaced under section 22, the revised or replacement policy statement.

(3) The trustees must formulate any guidance given in the policy statement with a view to ensuring that the functions will be exercised in the best interests of the trust.

(4) The policy statement must be in or evidenced in writing.