John,
It seems fairly straightforward to me.
http://www.caa.co.uk/docs/175/srg_lt...ection%20D.pdf
Section D4.5 Conversion of a non JAA professional licence to a JAR-FCL CPL(H)
If you hold a current and valid CPL(H) non JAA, issued in accordance with ICAO Annex 1, experience requirements pre course are as per JAR FCL 2.155 (b) and (c)
155 hours as a pilot in helicopters, comprising 50 hrs PIC and 10 hrs cross country.
The total hours can be reduced to 105 if you hold a CPL(A), and 135 if you hold a PPL(A).
You hold a non JAA CPL(H), if thats current and valid, as a PPL (A) holder it seems you can reduce the required heli hours to 135. Simples.
You also need a valid JAA Class 1 medical, and the theory passes.
CPL course is training as required/deemed necessary by an approved FTO. If you don't hold a night rating you'll need the 5hrs etc of night training as per JAR FCL 2.165 (b)