You can blame the Tories and Labour in the 80's and 90's.
The Tories saw immigrants from Pakistan as being natural Tory voters (what with the small businesses and everything) so they parachuted them into depressed former industrial areas which normally voted Labour.
That lead effectively to ghettos of people from the same place all having very little need to speak English or adapt to local customs.
New Labour did nothing address this and the Liberals, BNP and UKIP go out of their way to exploit it.