When choosing a UK casino with many high RTP slots, start by checking the size...

https://www.insert-bookmark.win/when-choosing-a-uk-casino-with-high-rtp-slots-remember-rtp-is-a-theoretical

When choosing a UK casino with many high RTP slots, start by checking the size of the game library and the reputation of software providers. Remember that RTP is a theoretical average, not a guarantee