4.—(1) The rules of law referred to in section 171 of the Act continue to have effect in relation to criminal proceedings commenced before 25th June 2012.
(2) The common law of diminished responsibility continues to have effect in relation to criminal proceedings commenced on or after 25th June 2012 where the conduct giving rise to the proceedings took place before that date, the case proceeding as if—
(a)section 168 of the Act (in so far as inserting section 51B of the Criminal Procedure (Scotland) Act 1995(1); and
(b)section 171 of the Act (in so far as abolishing the plea of diminished responsibility),
had not been commenced.