Aha! Thanks so much Littledumptruck and everyone else who took the time to help me. The throttle cable on the offside had been disturbed from where it enters the junction box under the centre of the frame. Meaning the throttle was about half open on this side all the time when trying to start. Problem sorted and she runs like a dream again.
Going back to the root cause of my breakdown, the moral of this story is that if you replace fuel lines in the tank, ensure the replacements are designed to be immersed in fuel, not just have fuel run through them. All sorted and a very happy man again.
Cheers all!