When choosing a UK casino with many high RTP slots, start by browsing the game...

https://wiki-aero.win/index.php/Virgin_Games_Casino_-_Is_It_Easy_to_Browse_the_Lobby%3F

When choosing a UK casino with many high RTP slots, start by browsing the game library size and the software providers behind the titles. Remember, RTP is a theoretical figure and doesn't guarantee wins