John McDonnell has said Labour can "convert" Jo Swinson to backing Jeremy Corbyn as leader as he said a no confidence vote is “unlikely” until after October 18.

Opposition party leaders will meet again on Wednesday as talks continue to try and stop a no-deal Brexit.

The parties are split over who could be installed as a “caretaker” leader. Jo Swinson has suggested Kenneth Clarke or Dame Margaret Beckett while Labour insists Mr Corbyn is the only option.

Mr McDonnell said: "The rules are the rules. We are not into a government of national unity.”

Asked if Ms Swinson’s refusal to back Mr Corbyn has logjammed the talks, the shadow Chancellor said: "No. I was brought up a Catholic. I'm a great believer in the powers of conversion."

A spokesman for Jo Swinson responded: “Jo is a great believer in the power of mathematics. Jeremy Corbyn does not have the numbers and needs to make clear who he would support if we need an emergency government."

Chuka Ummuna, the Lib Dem MP, said: “Given 21 former Tory MPs and at least 8 others clear there are no circumstances under which they would vote Jeremy Corbyn in as Prime Minister then the numbers don't add up and an alternative compromise candidate will be needed.”

Jo Swinson credit: AFP

It came as Ms Swinson warned Mr Corbyn risks a no-deal Brexit “more likely” if he does not agree to back another interim leader.

The Liberal Democrats leader told the BBC: "The ball is now really in Jeremy Corbyn's court. Given he can't command the support of a majority, which candidate is he willing to support if we need an emergency government?”

However Ian Blackford, the SNP 's Westminster leader, warned the opposition parties’ failure to agree on a course of action meant they could run out of time to "bring down" the Conservative leader.

He told BBC Radio Scotland: "I do think there is a danger we run out of time, because when we call a motion of no confidence we have 14 days to put an administration in place. Once we get to the middle of October the options for us are beginning to close off.

On Tuesday Labour requested a meeting with Sir Mark Sedwill, the Cabinet Secretary to clarify how the next stage of a confidence vote would work and how a new leader would be agreed.

Meanwhile Mr McDonnell said the so-called “Rebel alliance” is "trying to get clarity when we go for a vote of no confidence. Obviously we wait to see what comes back from the European Council and the discussions there."

Asked if it could take place before Oct 18, he said: "Unlikely".

The shadow Chancellor also expressed concern Mr Johnson would defy Parliament if he lost the vote.

"What happens if Boris Johnson squats in Number 10, refuses to budge etc?” he said. “How do we then demonstrate, what mechanism is there available to us to demonstrate confidence in an alternative?"

Mr McDonnell said Labour wants to “get the ground rules sorted" with Sir Mark. A Labour source added that the Fixed-Term Parliaments Act is “untested” and that further clarification of what happens if the Prime Minister loses a no confidence vote is needed.

John McDonnell and Jeremy Corbyn credit: PA

On Monday the opposition leaders agreed to spend this week trying to force the Government to publish a series of sensitive Brexit-related papers, with the Liberal Democrats expected to table the motion in the coming days.

However, they failed at the first attempt on Monday, when John Bercow, the Commons Speaker, refused an application from the SNP to try and secure the Government's informal proposals to the European Union on a new Brexit deal.

Mr McDonnell also told reporters Dominic Grieve and Sir Oliver Letwin are looking to "close down" ways the government could be getting around the Benn Act, which requires Mr Johnson to ask Brussels for an extension if he cannot get a deal by Oct 19.

Mr Grieve yesterday told the Telegraph the Act is “fit for purpose” but that he remains “vigilant about what the government might do” following reports it could try to circumvent it.