There's a lot of services that aren't available in the UK, but the best available one I've seen so far is probably Disney, because they own literally everything, they don't have to worry about license costs and expirations. At least they can keep what the do own up on there, while still creating new things to expand upon the library. Amazon and Netflix seem like dumping grounds and a big game of musical chairs.

Funnily the best service over all that I have heard of is a Russian one called Kinopoisk. It's like their own version of Netflix but actually has everything.