Thanks for all the info.
Yes, I think I'll definitely go down the heliocoil route. The cost of getting a new head and the amount of miles on the clock doesn't really make it a good option yet.
I live just outside Oxford (ironically I work just around the corner from the BMW mini plant!).
I live in a town called Carterton, Oxfordshire so if anyone can recomend a mini garage?
Also, would it be worth approaching precision/light engineering company or would a gagage be just as able? (heliocoil).
Thanks for your help guys