The biggest minorities in the UK are the Irish and Poles. Somehow, it is still probable that the Catholic minority might grow in the UK as Poland is in pretty dire straits.Thanks for the reminder; it seems that Pascoe forgot. As recently as when I was there, 25 years ago, the Catholic Church there was largely Irish; since Communism fell and the Irish have lapsed/assimilated, the church there has changed from "the Italian Mission to the Irish" (snotty Anglican joke) to "to the Poles." One of the nicest groups to come to America and I'm sure that's true there too.
To be fair to Pascoe, relying on immigration isn't a good growth strategy; it's not evangelism. Witness Eastern-rite churches in America, Orthodox etc. as well as Catholic. They mostly die out by the third generation here, due to assimilation. I'd love it if American Catholicism were Byzantine instead of Novus Ordo, and that option offers imaginative yet small-o orthodox answers outside of usual traditionalist thinking, but it just isn't happening.
That wasted potential is also why it's so sad that so many putatively Catholic online "apostles" for the Christian East attack the church's teachings. They are few; many/most such leave the church, which at least is honest. I think being an unlatinized Eastern Catholic who's actually faithful to the magisterium is one of the hardest callings these days, and yes, some Latin Catholics are called to make that change; I think Sheptytsky should be named their patron saint.