It's more popular in Ireland than the UK. The UK has a couple of country radio stations, but most parts of Ireland (especially in the rural west) have at least one country daypart on their main local radio station. Midwest Radio in Mayo plays a lot of country.
In Ireland on the radio, they mix American country with "Country and Irish", which is a sort of hybrid country-folk genre, often traditional songs or Irish covers of American country songs.
I was driving through Northern Ireland a couple of years ago, got close enough to the Irish border and radio from the other side started crackling in, and this was the first thing I heard! I've always liked Irish radio, it's very distinct from UK radio in a good way. It's a lot more "human", less corporate, there's a feel of a real live human playing songs for the people.