The next bit to check was the rubber rings that separate the plates. These were all intact but, while playing around with the clutch basket, I discovered that it had some movement on the shaft. Further investigation revealed a hand-tight centre nut AND the tab washer on the wrong way round! The other problem was the size of the nut – 29mm, not a standard size in the toolbox. I suspect that the last person to have the bike apart couldn’t tighten the nut up correctly because of this, and compounded the problem by putting the tab washer on back to front, hence the loose basket. This was obviously the cause of the horrendous clutch action