All this talk of Disney/Universal etc building, whilst its true that's it's very unlikely to happen, I think it's also very sad that it won't. Yes, we have tight planning controls and large masses of green belt, but the controls are nearly almost as strict in Paris.
The UK is such a widely ignored country for these developments, and think of the money they would bring in if they were to happen. Tourism would shoot up, and decent parks can be built whilst still maintaining a 'British' feel. With the right mind, and the right people behind them, Disney and/r Universal could easily tap into the UK market, particularly as most Brits can't afford to travel half way across the globe for the experience.