Andy I cannot believe the clutch plate was stuck to the flywheel. If that was true, the gearbox input shaft would be constantly spinning and you would not get it into gear because the shaft would not slow enough to allow the synchro rings/gears to align and mesh.
It was easy to free off. What was strange was that if I'd left the car for some time it worked fine when I put it into gear initially, but if I only left it for a short while it would stick - almost like the heat stuck it. All resolved now.