No way they come back from that.
The population of England is ~56 million, so 3 million is ~5.4% of the population. They have not passed any point of no return, and Brexit will help to stop forced immigration.
You are watching the overthrow of Western Civilization in slow motion. It is a sad statement, but nothing short of a fight will resolve this.
Brits are hasbeens. Muslims have the vote and Brittain will turn into a third world country. They have turned Africa, North of the Equator, into a third world country.