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

https://lima-wiki.win/index.php/What_Are_Responsible_Gambling_Interventions_in_UK_Casinos%3F

UK online casinos operate under strict rules set by the UK Gambling Commission to ensure fairness and player protection. They often offer games with a minimum 96% return to player (RTP), meaning most bets are returned over time