Takes about 5-6 turns to get going.

Get a small amount of smoke from the exhaust on starting.

A lot more than the 1996 Passat I had which started after a max of two turns.

So should I be concerned, is the timing out or does it need checking?

Cam belt was changed in December 2009 at 100k, now 150.

I have VCDS lite so I can't check the timing.

Glowplugs show a resistance of 0.7-0.8 Ohms.

Full service in Jan 15. The advice was to change the cam belt every 80k.

 

80k is actually a fair bit for the belt and associated parts. We tend to think in terms of 4-6 years and I'd be very wary about taking one passed 50k. Think vw advise 60? Not totally sure on diesels though. Anyway I reckon it's due and heading towards pushing luck, whether this is associated with your starting issue though I'm not sure, certainly won't help. Certainly worth checking timing, but even.more worth getting the belt done I'd say.

Check condition of the usual suspects, battery, starter motor and alternator.