Hi Gareth,
Thanks very much for the response: I'm really glad to hear you think it's a bit early for DMF/Clutch issues, but hope that doesn't mean it's something much harder to solve!
I bought the car at the end of August from a private seller (through gumtree). I realise the risk involved there, but I met with the guy at his home on a few occasions: he was selling because he had a new baby (I saw the pregnant wife on one visit and the newborn on another!) and he needed something bigger for his family of 5. His whole story checked out, he has a full service history from a local Audi specialist, it appeared to be immaculate and he seemed genuinely sorry to be saying bye to the car. If he was scamming me then he's very thorough!!! He had it MOTd the day I took it off him, and looking through the MOT history everything looked fine -really consistent 8000 miles or so per year, only one or two times with fails and passes the following day etc. etc.
It felt like it was running like a dream for the 6 weeks or so I've had it, but I do at least 80 miles a day on my commute, so I've put nearly 2000 miles on in that time... I'm not sure if it was doing only stop/start city runs or not for it's recent past, but we are living in Edinburgh so it's possible that city driving has been the recent history.
I've booked in with another Audi/Volkswagen specialist tomorow morning, so I'm hoping they can diagnose the issue in person. I've driven it to work the last two days (another 150 miles...) and it appears to not be worsening for the moment. In fact the vibration while idling seems slightly less, but steady. There's the slightest falter when starting (and yesterday it took 3 attempts to start on one occasion after refuelling, but that just happened that one time). While driving the vibration/shaking isn't pereptible, unless in 6th gear at slower speeds and very low rpms (when I should have downshifted anyway...).
I understand this is not enough to go on without seeing the car, I just thought it was worth posting in case someone might say "I had exactly that issue and here's the solution". If I get the answer I'll post it here in the hope of helping someone else in the future.
Cheers,
Glen