Thanks for the replies guys.
Tried the car again with the cam sensor disconnected and it started fine. I can only assume that the first time I tried it the engine was flooded.
Further developments were that it had been to another garage for the engine light being on and they fitted a new cam sensor. I suspect that possibly the light had been on for some time and the car was still starting because the cam sensor had failed. So fitting a new sensor cured one fault and manifested another.
I hate it when others have been at a job first as the waters get so muddied.