It feels as though the clutch pedal is much softer than it used to be and has to be depressed all the way to the floor to shift and it is more difficult to get into gear, particularly reverse.

Could I have more information please? What exactly do you mean by "Suddenly stopped working". Use the Comment button below and I'll try to give you more help. Does the pedal feel the same when you press it or has it changed? Softer, harder or sinks to the floor and won't return to the start position? Are there any strange noises when you press the pedal or try to shift gears? Noises like grinding, crunching or squealing?
Loss of clutch could be a few things. The fluid level could be too low so the thrust bearing inside the gearbox housing can't push on the clutch mechanism. Check your Brake Fluid Reservoir levels as this fluid is for both the clutch and the brakes. There could be an air bubble in the fluid pipes causing an 'Air Lock'. An air bubble means the fluid isn't moving no matter how hard you press the pedal.
There could be a worn part in the clutch system that's slipping or broken preventing the clutch from working correctly. On average, in normal use, a clutch can last about 60 thousand miles before it can give problems. Some driving styles can be rough on clutches so they can wear out faster.
Please comment with more information and i'll see if we can work out what the problem is.

Master or slave cylinder blew out. Could be the pressure line also.

A clutch pedal normally does go all the way to the floor. If you can shift gear without a crunch, it is disengaging OK.

The loss of power could mean the clutch plate is worn and is slipping when engaged. There is a crude test for this. Start the engine and idle it. Apply the footbrake firmly, depress the clutch and put the gearbox in 3rd. Let the clutch out slowly. If the engine does not immediately stall, the clutch needs replacing.
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the reason for hard shifting and selection when running is that the clutch shaft ( input shaft) is still turning even though the clutch pressure plate is released
it can be from oil/grease on the fly wheel /pressure plate face causing it to stick when hot
it may be from sticking clutch plate on the splines binding when hot
or it could be a dry spigot bush or failed bearing in the end of the crankshaft that positions the clutch shaft
check the pedal height adjustment and the position it is from the floor when starting to engage
It may be adjustment under the dash

check for throwout arm adjustment also..(tighten the cable if ends are good)

these are very hard to bleed, also check your fire wall for damage where the clutch master bolts up. another thing is take a good look at the clutch pedal asm, the frame sometimes wears and cracks so you loose a little pedal travel.another thing is a bad preasure plate,spring breaks on plate,

The clutch master has blown out

if the pedal got lot of play if its hydrolique air in the system or missing oil brake fluid goes in the reservoir pierre

how does the clutch pedal feel?..clutch out of adjustment,needs clutch job...kev-mn.

If it is a brand new clutch, it's not broken in yet, which is why it "sticks". Give it some time, though, and it will stop "sticking". It took a half mile of stop and go traffic for mine to stop doing that with my new performance clutch.