Nick Boles is half-right.
The United Kingdom, being a multinational state, has never been as homogeneous as Sweden. But controlling immigration, and the wider task of resisting capitalism and globalisation, is in fact the only way to maintain the distinctiveness and diversity of four countries in one, in all four of which the old landed class has a different ethnic background from everyone else, one of which contains all three types of the Irish (one of those types hardly exists anywhere else in these Islands), at least one of which still has two thriving indigenous languages with distinct cultures accordingly, and so on, and on, and on.
The Swedes are happy both because of their social democracy and because of their immigration controls. You cannot have the first without the second. And that is a very good argument for either by reference to the other.