Some Safeways stores carried Irish brands don't know if they still do, otherwise go to a area where there is a large Irish community as some of the stores tend to stock what's on demand
You can come to the end of my road in Tooting; there's an Irish mini-supermarket that sells Irish goods (and little else). So if it's Taters crisps and soda bread you're after, Tooting's the place to be (I realise that this is not helpful if you don't live in south London).
sainsburys sell irish cheese, irish bread and sometimes they also have irish meat, the irish whisky in their is also nice, tesco sell barmbrack and soda bread and have a range of cheese and organic irish butter,birmingham outdoor market has a stall selling the lovely floury irish potatoes, and the irish centre is just down the road from the market, and they have a shop inside, selling irish gifts,,,mullein