Now that the UK has voted to leave the EU, we are currently in the "transition period," which ends December 31, 2020. After that period, many new rules and regulations take effect, including rules governing the visas required for touring artists. Starting January 1, 2021, EU musicians (and other artists/athletes) will require a visa to tour the UK under a points-based immigration system. This is the same system that bands from outside the EU currently use when applying for a visa to tour UK.
The tier 5 requires a £244 application fee and a certificate of sponsorship. Prior to the new rules, EU artists could travel to UK without any visa or fees required.