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Downing Street is braced for further resignations after Boris Johnson’s brother Jo sensationally quit over Brexit.

Sources say three ministers are in “advanced talks” to follow his lead and plunge Theresa May’s government into fresh turmoil.

One insider said: “They are ­planning when exactly is the right time to do it. Jo set the news agenda by releasing his decision on Friday evening. Everyone was a bit surprised.

“The logical thing to do would have been to quit after the Brexit Cabinet meeting. So it’s important they get this right.”

Mr Johnson, who backed Remain during the 2016 campaign, quit his role as Transport Minister.

(Image: AFP/Getty Images)

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In his resignation statement, he said he believed the public should have a second referendum.

And he blasted the PM’s handling of Brexit negotiations. Mr Johnson is the sixth minister to quit over Brexit since Mrs May’s January reshuffle.

Three were Leavers, including Boris. The others were Remainers.

Mr Johnson’s decision piles more pressure on Mrs May, who faces a crunch week in Parliament.

Tory MP Anna Soubry, also a Remain campaigner, said: “Jo isn’t the only minister who shares these views and I hope others will follow his lead.” One insider said: “We know there are three ministers in talks but it will be interesting to see what the Cabinet does.

“Andrea Leadsom and Esther McVey will be thinking about it. And then Sajid Javid and Jeremy Hunt will be having a look at their positions.

“In some ways Dominic Raab is the key one. If the Brexit Secretary goes – again – what does it say about the whole process?” A backbench source said Jo Johnson’s departure was a “real blow” for Mrs May, adding: “It shows there is another front opening up. We all knew the Brexiteers who have dug in and are prepared to vote against whatever deal she brings back from Brussels.

“But now you have a fresh set of Remain people who are equally ­hardline when it comes to the ­negotiations. This is real trouble.”