Kent would be a perfect location. Especially if based not too far from the Channel Tunnel or ferry ports so people from Europe can get there easy. Also the M25 and London wouldn't be too far away, so there would be multiple transport options. (I Know Chessington, Thorpe etc aren't too far from Kent, but far enough).
Personally I'd love Universal to start a park in the UK to challange Disneyland Paris. Alot of Universal rides are based indoors too, which would hopefully mean it could open all year round.
Just imagine having rides as good as Spiderman and The Mummy here in the UK.
Sadly I doubt they'd do it as they seem happy to market Florida as the theme park heaven from us Brits.