Sorry a3derv1 I don't have the part numbers to hand, just asked for centre caps for RS6's and tried one at the dealer before committing to a set.
The wheels came from Rochford Tyres http://www.rochfordtyres.co.uk/ - very pleased with the wheels and tyres (Avon ZZ3's) but the after market centre caps were rubbish and I lost three on the first long drive after fitting the wheels.