Final Say: More than 400,000 people have signed The Independent’s petition calling for referendum on any Brexit deal

It comes as MPs from across the political divide backed the campaign

More than 400,000 people have signed The Independent’s petition calling for a Final Say on any Brexit deal secured by Theresa May.

It comes as MPs from across the political divide backed the campaign, including the former Conservative education secretary, Justine Greening, who wrote in an article for The Independent that the prime minister’s Chequers Brexit plan was “already dead”.

Ms Greening said that many MPs, including senior Conservative ministers, agreed that a new vote may be the only way to break the Brexit deadlock, as Theresa May’s wafer-thin parliamentary majority leaves her vulnerable to hardliners on both sides.

The campaign was launched in an editorial last week, which said: “The British people decided to pursue our course in the referendum of 2016, so as we now look for a decision on whether we will like the deal agreed with the EU (assuming there is one), it is natural that those same people should have the final say.

“Indeed, given the magnitude of the decision, it would be essential for the British people to be given that final right of approval, even if cabinet and parliament were providing the leadership we need, which they are not.”

Others to throw their weight behind The Independent’s campaign include the former prime minister Tony Blair, the Liberal Democrat leader and former cabinet minister Vince Cable and the ex-attorney general and senior Conservative MP Dominic Grieve.

In an article, published on Tuesday, Mr Cable said the campaign for a second vote has “momentum that will now be very hard to stop”, adding that he now believed there was a “very real possibility” that the government will be forced to call a vote later this year.

Former Labour cabinet minister Lord Mandelson – also a backer of the campaign – suggested that a fresh referendum could even empower Ms May to “stand up against Brextremists’ blackmail”.

He continued: “Of course, the Brextremists will call this undemocratic – that’s what they call anything that doesn’t help them get their own way. But the referendum two years ago instructed the government to start a negotiation for EU exit.

“It didn’t give it the right to make a shambles of the whole process, to be taken hostage by the Brextremists and then dish up a completely unsatisfactory outcome and demand that the country accepts it, whatever the cost.”