OPPOSITION leaders at Westminster have called on Jeremy Corbyn to join them in forming a united front against the Prime Minister’s Brexit proposals.

Ian Blackford, Vince Cable, Liz Saville Roberts and Caroline Lucas, who represent the SNP, Lib Dems, Plaid Cymru and the Greens, urged Corbyn to attend a summit tomorrow on opposing the Conservatives.

Theresa May pulled a vote last week on her draft withdrawal agreement on leaving the EU after it became clear MPs in her own party would help defeat the proposal.

Her decision, which angered euro-sceptics on her own benches, triggered an internal confidence vote, which she won despite over a third of her own MPs voting to bring her down.

Subsequent talks with EU negotiators, based on her wish to clarify the Northern Irish ‘backstop’ proposal in the agreement, collapsed after May and her counterparts failed to reach an agreement.

The Government has now said there will be a vote on whichever deal she presents to Parliament in January.

However, despite the disarray, the Opposition parties at Westminster have failed to agree on a cross-party strategy to put maximum pressure on the Prime Minister.

Both the SNP and Labour support a no confidence vote in the Government, but cannot agree on the timing.

The Nationalists and the Liberal Democrats also back a referendum on the final deal, while Labour has said a second vote is an option.

In a joint letter, Blackford, Cable, Saville Roberts and Lucas have asked Corbyn to attend a meeting in Westminster tomorrow to discuss the UK government’s current position on Brexit.

They wrote: “It is absolutely clear that the Government now is unwilling to give Parliament a say on the meaningful vote before the Christmas period. With recess fast approaching, the Prime Minister is running down the clock in a hope to offer a binary choice of her deal or no deal.

“While each of us hold many different positions, we share the common view that the Prime Minister's deal should be defeated and that a no deal should be removed from the table. There are other options and we must ensure that as opposition parties we put that challenge to the Prime Minister.

“No party can achieve a result that will deliver in the country's interests working alone. At this critical time, we must work together.”

Meanwhile, one of Corbyn’s own MPs has urged his leader to "come off the fence" and back another vote on EU membership.

Speaking to the BBC, Ian Murray, the MP for Edinburgh South, said he believed a call for a second referendum - or People's Vote - could command a majority in the House of Commons if supported by the Labour frontbench.

Other parties have been pressing Corbyn to call a motion of no confidence in May's Government. Labour, as the official opposition at Westminster, is the only party able to do so.

However, the Labour leader has ruled out the move, which could trigger a general election, until he can be sure of winning the vote.

Murray said: "The Labour Party will have to come off the fence on that at some point pretty soon because I think what they're trying to do might be incompatible with what's available.

"There's a majority of MPs that would stop a no-deal scenario from happening so that could be taken off the table.

"I think we can get a majority around a People's Vote because we need to try and break the impasse between now and the 29th of March."

Murray said cross-party talks in Parliament are ongoing to try and push for another EU vote.

"There's a growing number of Conservative backbenchers, and it's not just the usual people that are doing this in terms of supporting a People's Vote - we've got Guto Bebb who's supporting it, Jo Johnson's come on board recently. There's a growing number of Conservative MPs.

"So we do need to get the Labour frontbench into a position of a People's Vote and if we can do that, I think we can command a majority in the House and I think that's the best way to go.

"We've got to ask ourselves why we came into politics. I didn't come into politics to make my constituents and the country poorer.

"And therefore, given what's on the table is the worst of all worlds and given there's an impasse in Parliament, the public should be brought back into this process democratically."

Jeremy Corbyn said on Friday: “The last twenty four hours have confirmed that Theresa May’s Brexit deal is dead in the water.

“The Prime Minister has utterly failed in her attempts to deliver any meaningful changes to her botched deal.

“Rather than ploughing ahead and dangerously running down the clock, the Prime Minister needs to put her deal to a vote next week so Parliament can take back control.”