When choosing a UK casino with lots of high RTP slots, look for a large game...

https://mill-wiki.win/index.php/Why_is_RTP_Called_%22Theoretical%22_in_Casino_Games%3F

When choosing a UK casino with lots of high RTP slots, look for a large game library from trusted software providers. RTP is theoretical and doesn’t guarantee wins, but higher rates can mean better odds over time