thankfully seems to be running fine now but cant tell for sure what fault was, While i was waiting for injector seals i removed egr valve as local audi dealer said they had egr faults with these engines causing non start not sure how egr can prevent start up but while i was checking operation with modis component test i made the mistake of working the small butterfly flap by hand and it slipped on the spindle!so had to replace egr valve.when i reassembled with new inj seals and egr valve it did not start straight away but gave it a sniff and it fired up and has run perfect ever since!
so not very conclusive unfortunately. audi dealer did also mention they had seen cases of these engines with faulty crank sensor with no fault code causing non start.
thanks for all youre help, will post again if any more trouble.
jon"s point about the fuel temp makes sense i saw 65 degrees after a short road test.

graham.