Correction to my post above. The CAA have now re-assured me that when Part-FCL.600 says
Operations under IFR on an aeroplane, helicopter, airship or powered-lift aircraft shall only be conducted by holders of a PPL, CPL, MPL and ATPL with an IR appropriate to the category of aircraft or when undergoing skill testing or dual instruction
an IMC Rating is now deemed to be an IR, so IMC Rating privileges are retained.
NS