UK online casinos operate under tight rules from the Gambling Commission...

https://zulu-wiki.win/index.php/How_Do_New_UK_Casino_Entrants_Compete_If_Game_Libraries_Are_Similar%3F

UK online casinos operate under tight rules from the Gambling Commission designed to protect players. They often offer games with about a 96% return to player (RTP), meaning a portion of bets goes back over time