Thought I'd give the latest update.
Initial thoughts from VW garage were that I'd bought a "dodgy" car which had a bent chassis. However, they've now done a full test (wasn't called a T-VAC, but some other acronym) which they charged me £160 for, but the car came back as within the normal range (although they did say they did some minor re-allignment, probably to justify the test in the first place). However the car still has the same problem.
I've have now authorised them to do an additional hour's investigation at £70 +VAT (which they can't do til monday apparantly) but i think will concentrate around the steering and the suspension. Hopefully thats enough time for them to find the problem.
Also did some investigation into the cars history (At the garages request). Apparantly it did have a minor bump 18 months ago which had caused steering problems but has not had any problems since that was fixed and has gone through 2 services and MOTs (and 30k miles) since, so I'm not sure where the car has picked up the problem, but it appears to have occured after the car had finished its lease arrangement (in the last 30 days)
Hopefully the garage can diagnose the problem quickly, and get it fixed (and cheaply) as I still don't like the unknown!