I've had the same two warning messages come up last Thursday the 17th and thankfully this thread was one of the first places I checked and immediately stopped driving my car as it wasn't worth the risk of bigger scale problems down the line.
I live in Bolton and the brake pressure sensor wasn't available at Audi Bolton, nor in Liverpool where they said they had a few in stock so finally managed to locate one (Part No. A5Q0906207B) in Shrewsbury at a cost of £79.60 and got it delivered to me. Quite an indication of the widespread scale of this issue that the nearest part was 85 miles away but have managed to replace it myself this morning quite easily, again thanks to the help provided on this thread and the warning messages have both disappeared.
I've also emailed Audi Customer Services and am expecting a call back this week so hopefully they will take notice of this issue and do something about it.
