Well that's done the trick - no more cutting out at long last!
So it was a needle valve problem after all even though it acted just like an ignition fault until I actually saw fuel ejected. At least my ignition system is in better condition now with a new coil and better connections even though they weren't causing the problem.
Thanks to those who chipped in on this as it helped me think it through and stopped me going completely insane with frustration.