Everyone in this country should be made to speak English at all times - It's England so speak it.
If they won't them deport them. Too damn soft this country with immigrants.
Seriously?
I speak other languages (ok, one other

I speak English during my working day and with most of my friends. I know a couple of people who speak Hindi, like I do, and sometimes talk to them in that (though even our conversation is mostly in English). Now I should be stopped from being able to? Why? Perhaps I do want to talk about you without you understanding. That's up to me.
I agree that it's considered rude, but manners isn't something that the law should start mandating.
With respect to the Dominos matter - perhaps it makes sense to encourage staff to speak English while at work, but I don't agree with mandating it. As some others have said - as long as it is English being spoken to the customers, why does it matter?