If you dont mind a couple of weeks outside the UK then you can always do the FAA IR. The bonus being that on return to the UK you will get the IMC added to your UK licence for free (apart from the £64 fee that is!).
The course will set you back about £3000 which is much cheaper than the JAA IR, but be warned...its not an easy course to pass! Once you do have the ticket in your hand though its excellent, I always file IFR now when in the US, beats VFR any day
Julian.