The UK government is expected to finally formally table its offer on a customs union and protections for workers’ and environmental rights today in return for Labour’s support to get its Withdrawal Bill through Parliament.

But Labour’s shadow Chancellor John McDonnell has revealed the talks are close to collapse while former Defence Secretary, Gavin Williamson described the negotiations as a “grave mistake”.

The talks resume as May’s education secretary Damian Hinds said the upcoming Euro elections would be difficult for the Conservatives, with polls putting the new Brexit Party on 34 per cent – more than Labour and the Tories combined, currently at 21 and 11 per cent respectively. Ahead of the May 23 vote, two separate polls – by ComRes and Opinium – give Nigel Farage’s Brexit Party the biggest share of the vote with the Conservatives in fourth place behind Labour and the Lib Dems.

Brexit Party leader Nigel Farage coughs as he samples a Pinkman flavoured e-cigarette during a Brexit Party walkabout in Lincoln. Picture: Joe Giddens/PA Wire

Mr Hinds said: “I don’t think anyone is in any doubt these are going to be difficult elections for us – that much has been clear from the very start. For some people this is the ultimate protest vote opportunity. Actually, ironically this is, in a sense, for some people, this is the second referendum.”

The Prime Minister has also been warned of a Cabinet walkout if she strikes a compromise with Labour which would keep the UK in a customs union with Europe. International Trade Secretary Liam Fox has reportedly said a customs union deal which jeopardises new trade deals would be a “red line” for him - and it is believed that Jeremy Hunt, Andrea Leadsom and Chris Grayling share his view.

But Mr Hinds said there was no alternative to the talks. He said: “I disagree with Labour on many things... but there is some commonality of interest here. This is about our democracy, about our system and to repay the trust that people put in us we need to get things done for our constituents.”

However John McDonnell said the talks were on the brink of collapse, and said there was a growing sense of frustration with their progress. Mr McDonnell, who has been attending the talks with Keir Starmer and Rebecca Long-Bailey, said: “The problem they have is that literally in front of us they will fall out. So the exercise here is holding themselves together. And that is proving impossible. The administration is falling apart.”

Adding to the pressure on May, Sir Graham Brady of the powerful 1922 Committee of Tory backbenchers, is due to meet with her on Wednesday for “clarity” on her resignation timetable. Sir Graham, said he also expected the talks with Labour to peter out.

He said: “If the customs union is agreed without a second referendum then half the Labour Party won’t vote for whatever comes through regardless. And if a customs union is agreed then most of the Conservative Party isn’t going to support it. I suspect it will peter out in the next few days without any significant conclusion.”

Writing in a Sunday newspaper, Gavin Williamson, branded Mrs May “politically naive” for going into “fruitless” negotiations which he claimed were bound to fail. “Even if Labour do a deal, break bread with the Prime Minister and announce that both parties have reached an agreement, it can only ever end in tears. The Labour Party does not exist to help the Conservative Party.

“Jeremy Corbyn will do all he can to divide, disrupt and frustrate the Conservatives in the hope of bringing down the government. His goal, and he has made no secret of it, is to bring about a general election.”

Mr Williamson said the Prime Minister seemed oblivious to the fact many Tories believe she is “negotiating with the enemy”.

“There is a clue in their title: Her Majesty’s Official Opposition,” he said. “Their priority is to derail the government. Even if we get to a point where Jeremy Corbyn agrees a deal with the Prime Minister, when it comes to detailed scrutiny of the votes, Labour will revert to form. Even if it passes the first few votes, it will fail later.”

Mr Williamson said there was a simple calculation that a deal could pass with the combined votes of Labour and Conservative MPs, but “tough realities” must be faced if the deal was “far removed” from expectations.

Such a result could mean Mrs May has support from “less than half the Conservative MPs” including those “on the payroll”. That would lead to “knife-edge votes” and a “number of defeats” due to “up to 80” Labour rebels who want another referendum, he said, alongside SNP, Lib Dem and Change UK MPs who have pledged to vote against.

“This is when Labour will finally kill it, if they have not done so already. Labour will be able to credibly say it is not what was originally agreed between them and the Prime Minister. It is politically naive to go down this route.”

Warning Mrs May she was turning her own supporters against her, Mr Williamson said that scenario “should be avoided at all costs”.

“The Prime Minister needs to recognise that futile efforts to pull off this Labour deal are damaging us all. It is a grave mistake for any Prime Minister to fail to recognise when a plan will not work and it is fatal to press on regardless.

“We need to accept that these talks with Labour are fruitless and that not only will they not deliver the Brexit that people voted for, they are a betrayal of the direct instructions the people gave us in 2016 and 2017.”

He said in order to deliver Brexit, you need your “tribe” 100 per cent with you, as well as a “clear-sighted determination of what you want to deliver”, as opposed to “the lowest common denominator.”

Brexit talks resume as polls show surge in support for Farage’s party