@ecclefan: a reason is, that Britain is an Island and the cars are RHD - so the prices for used cars weren't hold up because of the Export.
Indeed, prices for used cars are lower in the UK than in Continental Europe (the most other things in the UK are much more expensive than in the Euro-currency-zone)

By the way: just this moring I saw a Polish truck, loaded with used British cars, Vauxhall's and Peugeot's, going eastwards on the Autobahn.