I know some people will disagree, but Blackpool Pleasure Beach and Alton Towers aren't too far away from being world class. After a period of losing money, Blackpool are just about in profit again. If things go well with their Mack launched coaster then there's some real potential there. Not to be a Universals or Disney kind of park, but a world class collection of historic rides with a few world class modern rides (Valhalla is one of the best water rides out there). After a period when several 'classics' were destroyed and they added a second hand SLC I think some people did lose confidence in the park, but it's not too late to turn things around and if they get this next coaster right, it will be a big start.
I'd say that Alton Towers does have a world class setting. It's hard to think of a vista that's as impressive as the Towers or Gardens. Some of the rides at Towers probably are world class too. Particularly Nemesis and Hex. To be considered world class overall they probably do need longer opening hours, more live entertainment and a couple more non-coaster rides, but both Towers and Blackpool could both be seen amongst the world's top theme parks.