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Jeremy Corbyn now faces pressure from both the left and right wings of his party on Brexit, after a top union official said backing a Tory divorce deal would be “unacceptable class collaboration.”

It comes as the government’s Brexit plan slid further into chaos, with David Davis’ new plan for the Northern Ireland border was branded “fantastical” by critics.

Under the plan, Northern Ireland could be given joint EU and UK status and a "buffer zone" on its border with the Republic.

Lib Dem Brexit spokesman Tom Brake dismissed the plan as being "like something out of Alice in Wonderland”.

Labour MP Chris Leslie, a supporter of the Open Britain campaign against a hard Brexit, said: "If there was an award for coming up with unnecessarily complicated and convoluted solutions to self-inflicted problems, David Davis would win it every year.”

Jeremy Corbyn already faces firm opposition from the centre-right of his party over Brexit, with a string of moderate MPs backing a second referendum on the terms of the Brexit deal.

(Image: AFP)

Last night, a cross-party group of MPs, including Labour members from across the party spectrum, signed a joint letter calling for an option to remain in the EU to be included in parliament’s meaningful vote on the terms of Theresa May’s divorce deal.

The letter, organised by campaign group Best for Britain, was signed by a string of prominent Labour MPs including David Lammy, Tulip Siddiq, Wes Streeting, Mike Games and Neil Coyle.

And the Labour leader (FRI) faces fresh pressure from the party’s left wing, as a prominent union leader urged him to “come clean with the electorate [and] say the Brexit squeeze ain’t worth the juice.”

Manuel Cortes, boss of the transport union TSSA, warned Brexit would leave Labour’s working class supporters worse off.

(Image: Daily Mirror)

He was speaking at the launch of new campaign group “Labour Against Brexit”, which called on the party to realign towards a Remain-backing position.

While they will not call for a second referendum, the group say Labour coming out firmly in favour of staying in the EU will give voters a clear choice at the next election.

A tour is planned for the summer with speakers including Mr Cortes, Labour MEP Julie Ward, former shadow minister Catherine West and Green party co-leader Caroline Lucas.

Mr Cortes said: “There is nothing about Brexit that will make life better for the working class.

“It was a rightwing brainchild won – and only narrowly – on a deceitful programme of dog-whistle racism and the big lie that the NHS would get £350m a week.”

He added: "The left should unite now and come together to stop this Tory act of war against our class. Our job is always to defend our people against the boss class.

“Supporting Tory/Ukip Brexit is unacceptable class collaboration. Full stop."