There's a fine line to be trodden by convertible cars and for my money, the Audi A4 Cabriolet stands astride it like a colossus in a designer frock. On one side of the Audi, you have family hatchbacks and superminis with their roofs scythed off. They're cheap and reasonably cheerful but hardly the last word in elegance. On the other, are the real show-off machines. The sky's the limit on price and luxury with these but they're only likely to collect jealous sneers and the occasional hurled drinks container on the average British high street. The A4 Cabriolet manages to appear cool, yet classless, a neat trick that makes it a desirable used proposition and not just for image-conscious ladies of a certain age.