Well my clutch was really hard for about 1000 miles, but then pretty suddenly went really soft, and displayed exactly the symptoms you describe. Within 20 miles the clutch had gone.
When the clutch was looked at, there was found to be no fluid in the master cylinder so if you haven't already, check your fluid, and check in the footwell around the pedal for leaked clutch fluid!!
If indeed the whole clutch needs changing, then consider that you may need a new slave cylinder, which is an extra cost, and possibly worth doing considering that it's a relatively expensive job to open access the clutch.
The job itself may require the engine moved forward, or the gearbox moved back although some of the later defenders had chassis cross members which could be unbolted for access, which will make the job easier. (Mine is a 92 200tdi and it DIDN'T have the unboltable crossmember).
Another factor is the quality of clutch kit that's used. You can buy a mickey mouse one for 80 or 90 quid but if you do any towing or off roading, then expect to be having the job done again in the near future.
