I'm currently in dispute with my dealer and Audi about a similar issue to this. As it's still ongoing and may yet be resolved, I'll not go into all the details just now.
However, one of the difficulties I'm facing is that mine is allegedly the only complaint of this nature from any of the A1's sold in the UK to date. Basically I can detect a significant pull to the left at all speeds and on all straight roads. It is particularly obvious at motorway speeds. An example of this is when driving in the fast lane, if one loosens grip on the wheel, the car will almost immediately change lanes and continue to do so at which point it is wise to re-tighten your grip. Steering geometry has been checked so it's something else that's causing it. My car is a 1.6 TDi. Not sure if it's just my car, just the diesels, some of the diesels or all A1's that display this and would be interested in forum members feedback on their cars.