3. Have you ever been/gone to the UK?

Translation of the question: Вы когда-нибудь бывали/уезжали в Великобританию?

been is correct: the question asks about life experience. “Gone” would mean the person went there and has not yet returned.

Have you ever been to the UK? (Вы когда-нибудь бывали в Великобритании?)