I live in Chester. Not a very Catholic city.
The previous poster is right. Go to any Catholic church in the UK and start speaking to people and you'll hear plenty of Irish accents. More significantly, look through parish names and you'll notice the huge amount of Irish surnames.
Liverpool, Manchester and Glasgow were particular popular destinations for Irish immigrants. Due to the industry there and to those cities being on the Western side of Britain close to Ireland. Think of the amount of famous people from those cities that have Irish surnames (Glasgow - Billy Connolly, Frankie Boyle, Lorraine Kelly, Gerry Rafferty. Manchester - the Gallagher brothers, Caroline Aherne, Judy Finnegan. Liverpool - Jamie Carragher (up the reds), Elvis Costell - real name McManus, John Lennon, McGann brothers, Paul O'Grady and a load of others).
Liverpool has a "Catholic" population of 52%, this in a country where "Catholics" are only 10%.
I grew up in the Liverpool overspill of Ellesmere Port. In the Catholic school I attended virtually everyone had an Irish surname. About half of us seemed to have at least one Irish parent; both my parents are Irish. I remember thinking as a kid that everyone was of Irish descent.
Also, Lancashire was the heartland of the recusants. They were the people that refused to leave the faith and stayed Catholic during hundreds of years of persecution. I think people from a recusant family should be very proud. It also destroys the Protestant argument that people happily left Catholicism to become Protestants as we can see how recusant numbers grow the further away you get from the centre of authority (London).