Ned
The whole of the UK wasn't under water!
I'd be wary of buying from a garage/auction in one of the areas which were, though.
I know of a company here who bought in a transporter load of cars which were flood-damaged, and there have been loads of problems with the electrics, unsurprisingly.
I'm sure by now a lot of the cars affected will have been spread around the country so you should always be careful. If the car you're interested in was only 1 previous owner, who lived in Surrey, but the car is for sale in Leeds.....................
Look around for tell-tale signs - debris around the boot hinges, damp smell in the interior etc. Be careful, but you don't have to assume that every car in the UK became a lemon overnight!