Someone mentioned Salou above.
The theme park complex there is called Port Aventura and it is similar to Disneyland (in fact better than Disneyland Paris as the weather is better).
There is a huge theme park (on of the best I have ever been in), a huge water park, and 4 hotels on site.
If you stay at one of the hotels you get free unlimited access to the theme park and SOME free access to the water park (and reduced prices for other days).
You can walk from the hotels to the theme park and water park in minutes.
And being Southern Spain it is only a few hours from UK
More here
http://www.portaventura.co.uk/