Ok, I was just about to start stripping the starter off to have a look on the ench when we managed to get it started, we've discovered the trick is to only turn the ignition key a couple of mil rather than all the way & it starts like a dream! Turning it fully just gives a clunk like it's not getting enough juice. The only modification I can see is the auto choke has been replaced with a manual, very recently by the looks of it, can't imagine that could have an effect though? As it's going ok now, I'm just intrigued to find out if anyone has an idea of why?
Ta :)