have an issue with our 2010 Octavia VRS tdi (125 CR)

it had a few moments of rough running and then died at the lights. (trucked home mid arv Saturday)
It cranks over fine but there's no attempt to start.
No faults are stored (VCDS)
I've pulled the fuel filter and it's not full of dirt or water - looks and smells like clean diesel.

any ideas?