As is usual with unknown bikes there always seems to be another problem or two....or three.
The clutch was very heavy when operated so with the engine out it was time to examine it.
The tabs of the basket are very worn and this is probably causing the plates to stick when the clutch lever is operated. Now I could file them flat again however it is extremely unlikely that I would get each one flat and in the same position regarding the clutch plates. This would of course mean that I would be getting more pressure on some of the tabs and little on others. This would end in tears as the tabs that have more pressure would probably break and cause more to fail and then you have a bike travelling fast with lots of bits of metal flying around in the clutch. So I'm trying to source another basket or get this one professionally machined by someone who knows what they're doing.