I have a 1.9 JTD which had exactly the same symptoms. It turned out to be the pressure plate on the clutch. The splines had snapped one by one and eventually the release bearing actually went through the pressure plate. Hopefully this will not be the case for you.
You could try checking the hydraulic unit which is mounted on the gear box. Take 2 bolts out, take the cap off the brake fluid bottle as this supplies the clutch and the brakes. Press the end of the hydraulic unit in by hand it should move freely. The fluid level should rise in the bottle, when you let go it simply springs back out smoothly and the fluid level drops again.
You can get air out of the system by pulling out the metal circlip, careful not to loose it, it can fly off the end of the pipe. Pull the pipe back away from the hydraulic unit and fluid will come out of the nipple, don't forget to take the little rubber cap off the end, this reveals the end of the nipple. Keep the fluid topped up in the brake reservoir otherwise if it drops too low you will just pull more air back in.
The only other place I have heard of that can give problems is on the back of the clutch pedal itself. You may want to check this out. Why not get somebody to press the clutch pedal down and make sure that the fork on the clutch is operating correctly. If it is not working right it hardly moves at all, whereas when it is working OK it swings at least 1 inch on it's axis. I hope that this is of some help to you.
Regards - Geoff