Take a look at the Mazda MX-5. They lack the rarity appeal of the Daihatsu Copen but there's a reason they're so popular. £10,000 will get you a late third-generation model - you'll want the Roadster Coupe for the folding hard top roof. Alternatively, the Honda S2000 is a more serious sports car, but you might have to shop around a bit more to find a good one.