My understanding too - it has to be an actual IR certified helicopter. I imagine it is too ensure that you
a) get to operate all the bits of kit in an actual IR aircraft
b) can go into cloud for training
To be fair, if money was no object, then you'd do everything in such an aircraft....
Since A + B require a twin engine aircraft (you can't get the kit + fuel and pilot in an R22 for example, regardless of the single engine failure issues) most training gets done in a twin.
The 206 in Norwich is a "special" case.
Having done the FAA IR too, I think it's OK but a shame you don't get to try the real thing at least once on that syllabus. It seems to me there is a happy medium where you do some sim for procedures, some single engine Simulated IR for basic aircraft control and cheaper procedure practice, and perhaps 3 - 5hrs Certified IR aircraft at the end to pull it all together.
That shouldn't be too budget crunching (although still not cheap!). Bear in mind your first actual IR flying will be as a Co-Pilot anyway - no one will let a newly minted CPL/IR loose on a SPIFR ship in actual IFR!
As it is, for me with an FAA IR, the conversion will cost ~16000 UKP + VAT for a twin IR
BG