Britain has up to 1.2 million illegal immigrants, a quarter of all those that have unlawfully entered Europe, an authoritative study has revealed.

The number of illegal immigrants in the UK has doubled in a decade with more than half having lived illegally in the UK for more than five years and a third more than ten years, according to the pan-European analysis by the respected Pew Research Centre.

Only Germany has a similar number of illegal immigrants with between one million and 1.2 million, which means that it and the UK account for half of all those who have unlawfully entered Europe.

The research - the first study of its kind in a decade to cover all 32 European nations - exposes the scale of the migrant crisis and how Britain’s ineffective border controls have failed to stem illegal immigration.

David Wood, former head of immigration enforcement at the Home Office, said officials knew the scale of the problem from secret internal estimates which showed at least 150,000 foreign nationals enter the UK illegally each year and then disappear into the black economy.