(1)A person is not guilty of an offence under this Part if he proves—
(a)that he knew certain circumstances existed; and
(b)that it was reasonable for him to act as he did in those circumstances.
(2)A person is not guilty of an offence under this Part if he proves—
(a)that he believed certain circumstances to exist;
(b)that his belief was reasonable; and
(c)that it was reasonable for him to act as he did in the circumstances as he believed them to be.
(3)Factors to be considered in determining whether it was reasonable for a person to act as he did include—
(a)the seriousness of the anticipated offence (or, in the case of an offence under section 46, the offences specified in the indictment);
(b)any purpose for which he claims to have been acting;
(c)any authority by which he claims to have been acting.