When choosing a UK casino with a solid slot library, look for clear RTP info...

https://alpha-wiki.win/index.php/Blueprint_Gaming_Slots_-_Where_Do_They_Show_RTP_in_the_Game%3F

When choosing a UK casino with a solid slot library, look for clear RTP info since RTP reflects long-term payout averages. Some slots have varying RTP versions depending on the operator