I suddenly lost the drive and could only coast. I can select all the gears, clutch down or up, but nothing happens. Turbo Diesel Engine still starts ok, just won't move. Any ideas, thanks Steve.

Clutch is either worn out or stuck in the disengaged position - unless something dramatic has happened to the transmission, drive shafts, etc.

Ensure the parking brake is firmly applied, start the engine and select a gear and then look under the car to check if a drive shaft is turning.
If nothing is moving under there, the problem is either the clutch or transmission and at this stage it hardly matters which as the transmission must be removed to check the clutch.

engine starts but no forward or reverse gears

a manual gearbox
gear selection linkage /clutch / drive line failure

auto faults
low on oil
failed torque converter
gear selection linkage
drive line failure

If you are driving and you put the vehicle in neutral and coast, push the brake pedal and NOT the clutch pedal and see if the noise is still there. If the noise is there, then you will need to get your brakes checked out. If the noise only happens when the clutch is pushed in, then your clutch release bearing might have something wrong with it. I hope this info helps.

do they revs drop off when taking pressure off accelerator pedal when out of gear? if only staying high during gear change it would suggest a worn clutch friction/pressure plate so the engine isn't slowing down when clutch is depressed .I'd also have the OBD codes read to see if there is a sensor/switch at fault , but sounds like the clutch to me

problem with linkage cables. get under vehicle and select a gear
manually with engine off, then climb inside, start up with clutch
pedal depressed, release clutch, if nothing happens, problem in gearbox, if it takes off, problem with linkage cables.

Your clutch needs to be replaced.

I'm not a VW diesel expert, but you should have a switch on the clutch to prevent you from cranking the engine in gear. I would look for that switch and check for voltage on both sides with the pedal engaged.
There should be a small wire on the starter solenoid that goes to the clutch switch and then to the key.

no idea without a play,sorry i know this isnt the answer you need but without my head under the bonnet ? firstly try a new fuel filter and is the primer pump in the tank working ¿ if fitted as no year stated .is it common rail or a earlier version with a injector pump .Are you in the UK where bio muck is used for the diesel .

there is a plug connector on the top of the engine (you should be able to see it with the engine cover still on) check the wires going to the plug as they are known to brake

please let me know if this helps
cheers
big mike :)

Have you checked all the vacuum pipes around the top of the engine.?
It`s not losing oil pressure, it`s just about to stall when the oil light comes on.
Listen for a hissing noise under the hood.
Vacuum leaks can cause real problems with the inlet manifold pressures.
Good luck.