The UK may have decolonised most of its former possessions (let's leave aside the conundrum of Australia, Canada and NZ being Dominions for another post*), and leaving all the other cases aside, in the particular case of Northern Ireland the UK is still the Imperial metropolis. And Norther Ireland is of crucial relevance as one of the major stumbling blocks in the currency process.Overseas territories do not an empire make.The UK hasn't been an empire since the Commonwealth of the 1930s legally and certainly not since it lost most of its colonies since 1945. Northern Ireland is as much 'a colony' as South Africa was (Ireland as such was definitely treated as a colony by the British). Gibraltar was ceded by Spain; I'm sure Spanish nationalists consider it 'a colony', but its inhabitants would disagree (Spain holds similar territories in Morocco, by the way). The Falklands (Malvinas for Argentinians) are just some rocky spots with a few shepherds on it. Sure, it's a colony. (No Argentinians live there.) Cyprus: British military presence has nothing to with 'colonization': it was the result of the Turkish invasion and the delicate situation since (Cyprus was and is independent).
Does any of this make the UK an empire? Surely not. Those days are gone forever. Being an empire requires something more than some overseas spots under your control and a permanent UNSC membership these days.