"(3) The question whether the degree of force used by D was reasonable in the circumstances is to be decided by reference to the circumstances as D believed them to be, and subsections (4) to (8) also apply in connection with deciding that question. (4) If D claims to have held a particular belief as regards the existence of any circumstances - (a) the reasonableness or otherwise of that belief is relevant to the question whether D genuinely held it; but (b) if it is determined that D did genuinely hold it, D is entitled to rely on it for the purposes of subsection (3), whether or not - (i) it was mistaken, or (ii)(if it was mistaken) the mistake was a reasonable one to have made. (5) But subsection (4)(b) does not enable D to rely on any mistaken belief attributable to intoxication that was voluntarily induced."