Hi Tom,
Unlike the standard Mark series bikes, the Plus doesn't have a 'Ferodo' clutch plate - it has small round corks in an alloy plate. If the bike has been standing for some time, any dampness may have caused the corks to stick to the pressure plate and flywheel. I would suggest you adjust the clutch cable to remove any free play (to obtain maximum lift), then with the clutch pulled in, and the bike in top gear, rock the bike back and forth until the plate breaks free - then readjust the cable as normal.
This, of course, assumes that Dick has fitted a 'Plus' plate, and not an ordinary Mark plate. The 'Plus' clutches can be notoriously fierce in their operation and various owners have tried different methods of 'calming them down' - the most successful seems to be refacing the plate with bonded on cork sheet.
Hope some of this helps,
Regards,
Eddie.