2.0 140 TDI non-starter - swarf in timing belt cover

[Diamond Hell]

Pulled up yesterday and noticed an odd rattle but it was running fine, after about an hour's drive - if it was an older car I'd say it sounded like the tin on the back of the timing belt cover was loose.

Shut the car off, came back out after an hour and it wouldn't start, tried to run a couple of times, then it did run, went to get out of the car park, whence it stalled under the exit barrier, so I rolled it back and out of the way - really wouldn't start this time, but turns over OK.

Ran VCDS, which said 000833 'implausible signal' on the camshaft sensor.

Timing belt cover off, showing swarf in the cover, it's steel swarf. The belt is still tight. The bolts on the cam sprockets, both centre and vernier are all tight.

The tensioner doesn't look like the bearing's collapsed - seal is still intact. What else might have collapsed? I see at least two other non-toothed pulleys in the belt run.

Anyone got any suggestions?

As I'm 250 miles from home and not too far from Autohaus Dolby I'm likely to get it recovered there and repaired, but any further diagnosis and suggestions for what to look at would be useful, please.