The flag of “United Kingdom of Great Britain and Northern Ireland” is the symbol 🇬 and 🇧 placed together. Not 🇺 and 🇰 – because that would make life too easy!

It’s because “UK” was reserved by ISO 3166/MA, back before the breakup of the Soviet Union, so that the United Kingdom and the Ukrainian SSR wouldn’t have a turf war over the combination “UK”.