The United Kingdom Civil Aviation Authority (CAA) has awarded Emerald Airlines (United Kingdom) an air operator's certificate (AOC) thus authorising it to fly domestic UK routes out of Belfast City.

Armed with permit AOC-2487, the British sibling of Emerald Airlines (Ireland) (EA, Dublin International) launched on December 7, 2022. It currently operates a single ATR72-600, G-CMJN (msn 1471), under the Aer Lingus Regional banner, connecting Belfast with Glasgow International and Southampton. The Irish AOC operates a further thirteen ATR72-600s, all of them flying for Aer Lingus.

For the time being, all other routes that Emerald Airlines operates for Aer Lingus out of Belfast (Birmingham, GB, Cardiff, Edinburgh, Exeter, Leeds/Bradford, and Manchester International) remain flown by the Irish AOC. The carrier recently told ch-aviation that it was planning to grow its Belfast presence once it had a British AOC.

Following Brexit, EU carriers can no longer operate domestic UK routes. As a result, Aer Lingus announced that it would terminate its only in-house domestic route from Belfast, to London Heathrow, in late March 2023. Although the Irish airline has established a sister carrier in the UK (Aer Lingus (United Kingdom)), it uses the AOC to operate transatlantic services from Manchester International and does not want to use it for short-haul routes. The carrier currently wet-leases an A320-200 from British Airways (BA, London Heathrow) to operate the Belfast-Heathrow shuttle.