Jim, Steve,
Thanks you were spot on, worn pulley and crankshaft. The garage put on a new pulley and warned the customer that a new crank was unlikely to be financially viable if the pulley should move again.
Horrible design with two flats instead of a key way, yuck! Usual rules apply though, it's only for location and not to do the driving so if the bolt stays tight enough it should be ok. The flange face on the crank seemed to be very small so that may be the root cause of the problem.
Didn't realise until I saw the pulley that it sends the ignition timing late as well.
Jim, what did you use as a reference for the timing light, are there marks on the flywheel?
Shaun.