It was making a bit of a racket, but the belt and tensioners were changed by the garage only 20k miles ago, so i guess they discounted it, and as the symptoms were similar to fuel starvation they referred me.
In respect of 'catching it in time', i had driven the car with this developing fault since February, and have covered over 5000 miles! Testament to the strength of the timing belt cover as this was the only thing restraining the belt from jumping off.