It's an "audi approved" used vehicle with a years extended "warranty". A warranty repair would consist of a completely new head and cam shafts to make it as new. A non warranty repair consists of smoothing the superficial damage to the head and replacing one of the camshaft, runners, and some seals and some plastic casing on part of the head: 5.5k versus 4k.
They have now said they will not do a warranty claim because its not component failure, which will be rejected. So the car will be getting the 4k fix and in the mean time working out who will pay. Fortunately the sales of good act 2015 is in my favour here. If the problem is reported within 6 months of purchase the onus is on the seller to prove the problem didnt exist at time of purchase, i.e. the car was fit for purpose at the point of sale. I can prove this issue certainly existed before I had any work done on the car mid november, otherwise nothing has been touched since the last service prior to purchase .... done by Cambridge Audi (vindis), who are notoriously a bunch of clowns with a bad reputation so I should have blooming guessed they would have been involved somewhere along the way.
They have already said about reducing labour rates on the bill to help me out. Its looking like I will have to pay something initially to get the car back, but my end goal is to pay nothing even if it means going to court.