Good UK sites: UKGC is the baseline. Clear RTPs set expectations. Check payout...

https://speedy-wiki.win/index.php/How_Do_I_Tell_If_a_Casino_Lobby_Is_Padded_With_Low-Effort_Games%3F

Good UK sites: UKGC is the baseline. Clear RTPs set expectations. Check payout times and delays. Seek simple safer gambling tools: limits, time-outs, self-exclusion