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

https://www.coast-bookmarks.win/uk-online-casinos-operate-under-tight-rules-set-by-the-uk-gambling-commission-2

UK online casinos operate under strict rules from the UK Gambling Commission that require transparency and player protections. They typically set games with an average 96% return to player (RTP), meaning the house keeps a set margin