The UK was one of the biggest proponents of the eastern expansion (2004 expansion) to take in Hungary, Poland, Czech Republic, Latvia, Lithuania, Estonia, etc. They were such big proponents that they didn't stipulate any national limitations on new members working in the UK immediately after accession, like most existing EU countries did. A move that, at the time, UK elite thought was illiberal.

The UK, little more than 10 years ago, was pro-immigration via EU in a way that seems inconceivable now. The UK's anti-immigration response today probably owes something to those decisions. Turns out those other EU countries knew a thing or two about immigration after all.