Hi
Also, have you tried measuring the voltage across the coil when using the starter?
Regards
Colin

When you say turns the engine over? Is that it attached and covering the flywheel, This issue we had is that the bendix broke and never engaged, although it sounded like the engine was Turing over, im sure you might of seen it if you looked inside the starter motor but I thought it was just worth mentioning. Hope,you solve this issue.

Ollie cox

Ok,
So we have isolated it to the switch panel switch having a broken connector and a faulty wire from the main power lead to the switch panel. Both causing intermittent fault. That was it.
The new coil turned out to be a duff ( Sod's law) which threw us, and the earthing has benefitted from a doubling up. One thing that did improve things was to put two 6v batteries in the tail wired up in parallel. Plenty of capacity, only had a 56aH battery before which might have been a bit low.
All in all, it's been a bloody nightmare!!
Thank you for all of your suggestions, all of them helped us eliminate various things and it confirms the total invaluableness of this support community.
Many thanks Tim
Austin 7 trialer (13 yrs and counting) - mainly thanks to the help received on this forum.