I mean I know the Warner Bros Studio Tour in Watford, fairly near to me, had plans to become a universal park, but it feels a little too late now for the land to be used for developments. The site is being used a lot for lots of Warner Bros films like the DC ones. Potentially, it would be a great place for a theme park with the M1/25 and Watford Junction nearby, but annoyingly, it most likely won't happen. I guess it will just be Harry Potter Studio Tour.
Universal allegedly considered a theme park not too far from this site but it was scuppered because concerns about the wildlife would have made getting planning permission extremely difficult.
The UK was also apparently considered for Euro Disney, can't remember exactly why it didn't happen (seem to have vague recollections of it being that the UK didn't fit the 'euro' image Eisner wanted)
New park projects often seem to get announced then never happen in the UK- there have been a few such cases including movie maker tie ins and big new projects that never got built- what's tripping so many of them up? Is it lack of space and planning permission issues, lack of investors or something else. It does get a bit disheartening looking forward to these exciting new projects then never seeing them happen.
As Chris said. We don't have vast amounts of land suitable for a major theme park and we have very strict regulations (with a very NIMBY minded population). Spending 10million designing a theme park only for plans to get delayed because a local resident pointed out a pond on the site has greater crested newts in it (sightings of a trespasser in wellies with a filled bucket was of course a coincidence).
You'd never get a Disney World situation where Walt was allowed to drain a swamp to build a theme park nor the shady dealings of Disney when it comes to the Anaheim local government in the UK.
Lastly, theme parks are incredibly expensive and very high risk. The London Resort is going to be built on the site where there used to be a water park before it went under.