Thanks again guys. I'm going to try and run with the cat. or throttle position sensor diagnoses initially. Harvey thanks for your suggestion but I don't buy the timing issue. When the pulley fell off (and it literally did fall off, not just come loose) I was able to rescue the car and drive it home with the pulley on the passenger seat, so the absence of the pulley had no affect on the running of the engine!

I will hopefully take it for an MOT test (annual roadworthyness test) on Friday as I can legally run the car on the road to/from the test centre and so get in a 10 mile journey there and back to assess the problem.

Will keep you in touch.