Thanks for your advice mate!! Took the car in today,showed the mechanic this thread & he read all the replys. So we've had a new valve fitted,he said he did 10 miles in the car then had it running for 30mins with no problems (although he said that when we picked it up Monday after we'd had all the other work done!!!). So tomorow i'll be testing it myself & i'll let you know how i get on.

Thanks to everyone again for the replys.