'You can be anti-antisemitism and anti No Deal Brexit', says Luciana Berger as she leads campaign to fight proroguing parliament

Ms Berger, who quit Labour over antisemitism in February, said: “We have to put our party political allegiances to one side at this moment of national crisis."

But reacting to suggestions the campaign would only help the Labour leader, the Jewish MP said this argument was "predicated on the preconception we still live in a two-party political system."

She added that fighting antisemitism and opposing Brexit were "not mutually exclusive."

Ms Berger said: “They are not in competition with one another.

"You can be anti-antisemitism - you can be anti a No Deal Brexit. And you can campaign and you can speak out against both."

Under Mr Johnson's plans, his new administration would hold a Queen's Speech - laying out the Government's plans - on October 14.

More than 200 MPs from all parties, excluding the DUP, have signed the declaration, which was launched with Labour MP Stephen Doughty.

The declaration reads: "Shutting down Parliament would be an undemocratic outrage at such a crucial moment for our country, and a historic constitutional crisis. 

"Any attempt to prevent Parliament sitting, to force through a no-deal Brexit, will be met by strong and widespread democratic resistance. We pledge to work together across parties and across our nations to do whatever is necessary to ensure that the people's voice is able to be heard."

Church House, which is close to Westminster, is where the Houses of Parliament met during the Second World War. It is a proposed site of a ‘People’s’ parliament in the event that Mr Johnson suspends the Commons.

The declaration was also signed by SNP Westminster leader Ian Blackford, Plaid Cymru Commons leader Liz Saville Roberts, Green Party MP Caroline Lucas and Change UK leader Anna Soubry.

Mr McDonnell said the campaign also had the support of his close ally Mr Corbyn but he was "trapped in meetings" so did not attend.

Asked how she felt sharing a platform with Mr McDonnell, Ms Berger said: “I shared the platform with Labour along with all the other opposition parties.

"We have to put our party political allegiances and concerns to one side at this moment of national crisis in order to stop a Prime Minister with no mandate subverting our parliamentary democracy."

She said that when he spoke the shadow chancellor "echoed what everyone signed on the declaration. Collectively we will work together to stop Boris."

Ms Berger said she was "very confident" enough Tory MPs would support the campaign to block a No Deal Brexit.

"Already a number of Conservative MPs have added their names and I expect more to do so. But it’s not just about signatures on this declaration.

"We know already from the parliamentary vote we had in July there is no democratic mandate for Boris Johnson to pursue a No Deal Brexit.

"Hearing from the speeches [at Church House] it’s very clear that  people have put their party politics one side to find that courage and do what is right in the national interest.

Liverpool Wavertree MP Ms Berger said: “The 20th-Century two party politics dynamic is fast evaporating.

"You only have to look at the plethora of recent polls to see that's the case. People previously used to vote according to a left/right axis. Now it's open versus closed. 

"That's why I support Unite To Remain, because at any future general election people will need to coalesce around one pro-Remain, open-palmed, internationalist candidate in each constituency.

“There are a number of parties that make that offer. Currently the Labour party is not unequivocally one of them."

She said she feared a No Deal Brexit could lead to a number of "potentially serious consequences" including around the battle against antisemitism.

"I think anything that seeks to make our country isolationist, separated from our neighbours, less open, less diverse  more closed to the rest of the world at a significant cost to our economy, is not a good thing," she said.

Ms Berger, who has continued with case work for her constituents throughout her maternity leave after the birth of her second child in March, said she was still to make a decision over what she intends to do at the next General Election.

As to who would make a better Prime Minister - Mr Johnson or Mr Corbyn - she responds: “Neither."

She addedd the prospect of parliament being suspended was “a historic constitutional crisis.”

But opposition leaders now have the option  of voting no confidence in the government when parliament when parliament returns next week.