UK online casinos operate under tight rules set by the UK Gambling Commission....

https://smart-wiki.win/index.php/Why_is_a_UK_Gambling_Licence_Also_a_Trust_Signal_for_Players%3F

UK online casinos operate under tight rules set by the UK Gambling Commission. These rules include things like a minimum return to player (RTP) of 96%, which limits how much the house can win over time