So, in practice, just how would english nationalists deport immigrants? I mean, what is the percentage of people in UK who want all immigrants deported? 1%? Probably less. Absolute majority of whites don't want that. Espescially city people.
Some may want to deport some newly arrived migrants and close the border. But those with passports will stay.Nobody is going to deport Emile Heskey or Amir Khan.

Let us summarize:

Facts
1. Majority of white people in the UK are very tolerant. They wouldn't want migrants to be deported or stripped off their fundmaental rights. This goes even for the patriotic crowd. To radicalize them you would need the situation to be much worse than it is right now.
2.The amount of immigrants in the UK is already huge. Even if the border is closed tomorrow, they would still outbreed locals(who breed badly and are aging fast) just not by 2050 but by 2070 for example.

Mass deportations most likely will not happen.

That leads us to the only conclusion-separate, create segregated state.