Chris, the simple fact is that there are many people living in say, Bradford, from Bangladeshi/Pakistani heritage (either born here or there) that cannot speak English, lots.
That's not to say it is exclusively them.
there may well be.
that doesn't mean they aren't or shouldn't be allowed to live here.
What matters is how many-'lots' and 'many' doesn't mean anything. How old they are, where they were born, the limits that their non english speaking places on them, their gender and so on.
If you can't speak the language of the country you have made home then you have limitations placed upon yourself and you are isolated.
People from places like Poland are taught nglish in school, people who immigrate, or originate in other countries aren't. Also many people who need the use of interpreters aren't immigrants but asylum seekers. I doubt whether learning English is the top of the priorities of people attempting to escape persecution.