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

https://blast-wiki.win/index.php/What_Does_%27Cost_of_Entry%27_Mean_in_the_UK_Online_Casino_Market%3F

UK online casinos operate under tight rules set by the UK Gambling Commission to keep play fair and safe. One key rule is maintaining an average return to player (RTP) of around 96%, which balances wins and losses