MPPCAG
EASA licence is required to operate aircraft registered in EASA member states. UK can't mandate that aircraft based in the UK be G-registered and operated on UK AOC for UK-EU routes, as that would be a violation of the traffic rights defined in the UK-EU TCA.
Just as British AOC holders can base G-regs in the EU (that will require a UK licence from 2023 onwards), similarly EASA AOC holders can base EU-regs in the UK.