Downing Street has dismissed Boris Johnson’s plan to let illegal immigrants who have lived in the UK for longer than 10 years stay in the country.

Asked about the “amnesty” proposal which Mr Johnson raised at a Cabinet meeting, a No 10 spokesperson said ministers would not be looking at the idea.

The Foreign Secretary believes the plan to give illegal immigrants legal status in the UK, would mean they can start working lawfully and contribute tax income.

It comes after the UK’s official forecaster predicted the Government will have to borrow an extra £122bn in the next five years in the light of weaker tax revenues and extra costs due to falling immigration in the run up to Brexit.

Asked whether Theresa May would consider the idea, the Downing Street spokesperson said: “It’s not something we’ll be looking at.”

Mr Johnson had originally proposed the amnesty during the referendum campaign, but at a Cabinet committee meeting chaired by the Prime Minister he restated the plan.

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A source told The Independent Mr Johnson had a “clear and strong” view on the policy and that he felt he had a responsibility to raise it given he had backed the plan during the referendum campaign.

In June he told a Vote Leave rally: “I'm not only pro-immigration, I’m pro-immigrants. And I am in favour of an amnesty of illegal immigrants who have been here for more than 12 years, unable to contribute to this economy, unable to pay taxes, unable to take proper part in society.”