Have a look in your owners manual at page 272/273 and 274, it quite clearly states the acceptable size for winter tyres approved by AUDI.

Your insurance company is probably trying to class it as a MODIFICATION and applying the "Chav just come from Halfords with Calos Fandango´s on his Saxo" Rule. But it is not a modification and is in fact an approved factory fit therefore your Insurance Company (and the AA) are unfairly asking you to "Risk Your Life" and "all who travel in your car in winter".

Plus you would not be able to fit Snow-chains on 18 -19 inch wheels, which if you like ski-ing in Europe, would render your car unuseable/illeagal on the the many access roads to resorts where they are often compulsory.

Dunk