So, managed to have s look last night, after dropping the torch and the batteries frustratingly falling out on more than one occasion i couldn't spot an obvious problem, had the case off the solenoids on the back of the engine, wiggled the wires around and although then engine didn't cut out there were slight changes in the smoothness of how it was running.
Couple of things I noticed - one of the solenoids was vibrating considerably in comparison to the others so slightly loose in its fitting, I removed all 3 of them, terminals are clean, then taped this down along with the others to reduce vibration.
Also, the alternator was vibrating badly- the lower mounting bolt was considerably loose and the one to mount it to the top of the engine- these are no all tightened and belt at tension.
Ran for 30 minutes last night and 45 this morning no probs, don't like jumping the gun but is looking like a loose connection somewhere!
Thanks