Going to try some photos from Photobucket on this post.
The problem with the clutch slipping seemed to have been caused by oil and dirt getting washed in from when I gave the engine a degrease. The clutch linings themselves seemed good for a few more years. It was noticed that the two springs in the clutch were not the same and that the rubber buffers were quite worn so it was decided to replace these while the engine was out.

New springs and rubber buffers. Many thanks to Neil Jarrett for the very prompt service.

Old and new buffer for comparison.

New springs and buffers fitted.