Don't know whether it helps but I have an old "EASA Approved" 355N Flight Manual Supplement which states "Though the helicopter is not certificated according to FAR 29 for Category A operation this supplement deals with the procedures and performance allowing the aircraft to be operated in a similar way". This particular supplement does not appear in later versions of the flight manual.
I also have a letter from DGAC which states "DGAC is pleased to confirm that the DGAC standard of AS355N is fit for the UKCAA Group A performance".