Right guys thought id bump this back up for one last cry for help..
collected the car from Oddkidd unresolved as i had enough waiting, seems ill just have to persist with this on my own at home.

to add to the list of things done, the cylinder head has had a full rebuild.

All i have left to try is send injectors off to be cleaned, and try a different crank sensor incase the new one i fitted was a dud.

Spark plugs were set to 6.5, i closed the gap to 6 but no better.

Any other suggestions? the car drives perfect at crusing revs but from 5k upwards it missfires, even when reved in neutral under no load.