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

https://mega-wiki.win/index.php/What_Does_It_Mean_When_a_UK_Casino_Must_Segregate_Player_Funds%3F

UK online casinos operate under strict rules set by the UK Gambling Commission. They often offer games with a minimum 96% RTP, meaning players get back at least 96p for every pound spent on average