Labour should set up a cross-party Brexit convention if the party gains power at the general election, Paul Mason told IBTimes UK on Monday evening (15 May).

The left-wing journalist said such an initiative would help Jeremy Corbyn establish new negotiating terms so that Brexit also "represents the wishes of the 48%" and the effects of splitting the EU are mitigated.

"The centre in politics has to decide whether it wants to stop Brexit or mitigate the effects. I want to mitigate the effects," the former BBC correspondent said.

"Because I cannot look in the eye people who in good faith for the first time in their lives voted, and their vote meant something I can't say to them, as some people want to, 'you were deluded, you were lied to'. We are always lied to.

"Brexit will happen because 17 million Brits don't want to be in the European Union."

Mason, who unsuccessfully campaigned for a Remain vote at the EU referendum, but also advocated reforming and revolting against the Lisbon Treaty, spoke at the launch of the Progressive Alliance alongside Labour's Clive Lewis, Green co-leader Jonathan Bartley and other prominent left-wingers in central London.

The tactical voting plan has been dismissed by Labour and the Liberal Democrats, but Mason said potential progressive governments will have to involve "some kind of informal coalition arrangements or alliances" for the foreseeable future.

"Once you look reality in the face and realise that the SNP is a perfectly progressive, almost social-democrat party, I would have no problem in principle of starting from the position of having an alliance with them in government rather than having it as a matter of expediency," the Labour supporter said.

"But those arguments have been overtaken by the emergence of a Ukip-Tory alliance.

"That is an alliance of the duped and the duper because many of the working-class people you speak to who were going to vote Ukip and have switched to the Tories do so because they think their wages will rise when all of the migrants are kicked out.

"We know that business leaders and senior Tories have no intention of kicking migrants out so it's simply an alliance based on falsehood.

"The danger we face when it all goes wrong [is that] it won't be those Conservatives from Kensington and Chelsea who are out there in the North of England and the Midlands picking up the piece as people get very, very angry about it."

Mason, speaking to IBTimes UK on the eve of the launch of Labour's general election manifesto, said he was "extremely happy" with the policies outlined in a leaked version of the document.

"It shows what Corbynism is and what it isn't," he said. "That programme would be very close to the Norwegian, Swedish or Austrian social democracy. It forms a basis for a working alliance between us on the Corbynite left and our colleagues on the centre-left of the party to make it work."

But with Labour up to 20 points behind the Conservatives in the opinion polls and Theresa May heading for a landslide on 8 June, should Corbyn stay on as leader after the election?

"I'm honestly not even in that mode at the moment, I was on the doorstep [in Nottinghamshire] and it didn't feel like a Tory landslide. I'm fighting for a Labour victory, but even if we get one I would be advocating for a cross-party alliance to run Britain."