Even if they go on a deportation spree to rid themselves of offending migrants, the population of naturalized Muslims is already enough to ensure Brits would be a minority. Their birth rate is low anyway, just like most of Europe.
It is not just the high number of births. The Muslim population in England is increasing due to a wide range of reasons. A lot of people are converting to Islam, mostly in prisons and drug rehab centers. Also, a lot of non-Muslim women are marrying Muslim men and then converting to Islam.
I also noticed that, even in my country it seems that their men are wooing Christian women in huge numbers that it almost seem coordinated. I won't blame them though. At the risk of sounding a bigot (can't call me racist, they look just like us) - they stink. Literally. Even the women, which I expect would have better grooming than men, smell like they don't use deodorants. Sometimes they'd smell so bad it would linger in the air several minutes after they left. I tend a store and after they walk away everyone in line would like "wtf!".

Non-Muslims here still have a decent growth rate though these Muslims would usually have 4 children or more (much more with more wives). Our gov't is considering a 2-child policy though I doubt they force Muslims to abide to that. That could be the end of us.