Good UK slot sites meet UKGC rules as a baseline, but that alone is not enough....

https://casinocrowd.com/if-a-casino-keeps-talking-about-its-licence-should-i-worry/

Good UK slot sites meet UKGC rules as a baseline, but that alone is not enough. Check clear RTP data, how fast cash-outs are paid, and whether useful tools let you set limits, take a break or get help when play stops being fun.