Easy226,
I remember reading about this last year on the CAA website. There used to be a 15 hour credit towards the IR if you had an IMC on an old UK licence but not if you had a JAA licence... yeah, another crazy rule but there you go.
Even if you had a UK licence now, the right to claim the credit for the IR ended last June if I remember correctly. There was never any credit for ground training.
Now this is the case, I see little point in paying for dual time training for an IMC if you're going to take the full fATPL training pretty soon. I'm sure others will disagree though, particularly the training schools!
Getting a non-JAA IR from an ICAO country (eg. USA) is an option to save money and have a jolly abroad. Then you'll just have to do 15 hours JAA IR training, which I found more than enough to get used to the different procedures in the UK.
Of course, you'll have to take the JAA IR exams too.