A UKGC licence is the starting point, not a guarantee of a smooth experience....

https://varimail.com/articles/best-way-to-find-slots-by-provider-on-a-uk-site/

A UKGC licence is the starting point, not a guarantee of a smooth experience. Check whether a site clearly lists slot RTPs, explains how long withdrawals usually take, and offers practical responsible gambling tools such as deposit limits and time-outs