Not so much stupid as deceived. The British Labour Party (The Left) imported the minorities from all the old colonies - which included Muslims from Pakistan - as a deliberate but secret policy, knowing that they would vote Left and dilute the power of the ethnic white native and autochthonous English (sound familiar).
Yup, this is the same exact strategy the American Democrat party has employed to great success. The conservatives have had their moments when it could have been stopped, but they catered too strongly to their business interests which wanted to import cheap labor.
There was one last opportunity after 9-11. Bush could have shut the borders down. We could have used that moment to slow the demographic changes - and we'd have had the support of a vast majority of the public. Too late now.