A6 2.7 TDI S Line Le Mans stalling problem

Hoping someone might be able to shed some light on this issue: 2008 A6 Avant 2.7 TDI Le Mans, been driving perfectly, no issues at all. Got in the car this morning and every time I let the clutch out the engine stalls. No, not my bad driving....

It's not mechanical - the gears change easily and you can feel the clutch bite, but as it bites, the engine shuts down, just like it's being turned off. If you're really careful you can keep the car moving just by slipping the clutch a little, but as soon as it bites properly the engine just shuts down. 

The engine starts and revs freely. No fault codes show up and no warning lights on. No funny noises or sudden jerk, just a straightforward engine shut down. If anyone could shed some light on this I'd be very grateful. Thanks!