Thanks Daniel & Terry, I will check the oil pump cable. My initial thoughts were of a locked brake. Since sending this post I have spoken to the previous owner who tells me that the bike has done very few miles since complete overhaul and has not been run in. So I now think that it was an engine seizure. I also think that the reason that pulling the clutch did not stop the skid was because the clutch drags badly, but I may be wrong.
Today I checked the clutch cable adjustment, both fine and course and it was perfect but the clutch still drags badly. I think the plates will have to come out and be checked. Unfortunately that will wait until next week.