Yes, if you get an FAA IR, the CAA will give you an IMC rating on the basis of it (not a JAA rating, only valid in UK) though unless you intend to get FAA licences, it might be an unnesessary expense as it no longer gives you much exemption from the JAA IR training.
I can't let the last remark go without comment. I am sorry the other chap did not get on well with Guildhall, I think he is being a bit unfair. I recently passed 13/14 JAR exams first time and the other at the next sitting & don't consider myself particularly intelligent or have foreign commercial experience.
Others in my group got all at the first attempt or dropped one. Some did drop a few more and have to resit them. The other schools may be very good, Guildhall is a lot cheaper though, they don't get the same amount of feedback questions that Oxford do which helps with their high pass rate. I doubt you could find a better Met lecturer in the country then Peter at Guildhall, some of the others are also very good, one or two could improve a bit, most do seem to care about students passing.