£500 is a good price point, especially if you're thinking of buying used, i've had some really great basses off ebay and this forum (musicman SUB bass, fender reggie hamilton jazz bass, G&L tribute l-2000, warwick corvette $$), none of which i paid more than £430 for, and most of which i paid a fair bit less than that! And they really were great basses, so don't limit yourself to new basses.
Even new, you have a good choice, there's a lot more available now than there ever has been and you can get a lot more bang for your buck, and £500 can get you a very nice new bass. I won't name any brand names because now would probably be a bad time to become biased to certain brands, all i'll say it, try everything in your price range, and i mean everything. Don't just try the classic fender p's and j's, even if you don't intend to buy something, at least try it. And certainly don't buy the first thing you see! Just buy whatever looks, feels and sounds good to you. Even if it is a squier! They're making some nice basses these days!!
Above all, have fun and good luck! Nothing like buying new bass