I'm not sure if it helps, but when I bought my S5 last year, since it was the first I had bought from a UK Audi dealer (my B5 S4 was a personal import), I asked questions about exactly how the 3 year warranty is provided and what the impact of using an independent tech for servicing would be. Ignoring the answer about servicing, it was confirmed that the first 2 years warranty is provided by Audi the manufacturer (i.e. VAG) because this is the minimum required under EU rules, but the 3rd year is provided by the selling dealer. I assume that extended warranty, although sold by an Audi dealer, is effectively provided by 3rd party insurance (even if said 3rd party is part of VAG). I assume from this that in the first 2 years there may be benefit in going straight to Audi UK in the case of a warranty dispute, but after that it may not help because it is the dealer you need to convince.
Having re-read your other thread I'm not sure who you are currently dealing with. Is it the original dealer that you bought the car from or another one? If another one they I'd advise that you are wasting your time. The T&Cs are clear (p7 in the reference given above, "Servicing requirements for your Audi"). However you do have a case for complaining to the selling dealer. Although "caveat emptor" is often quoted, in the case of an Audi franchise dealer it is reasonable for a buyer to consider that if a car is sold with warranty then there should be nothing about the car which would invalidate that warranty, otherwise it is a case of misrepresentation. Of course to get redress you may need to take the legal route...