Former foreign secretary Boris Johnson has called on Theresa May to postpone another vote on her Brexit deal, warning it would be “absurd” to bring it back to the Commons without first securing change from Brussels.
It was not possible that “anybody who believes in Brexit” could back the Prime Minister’s deal in a so-called “meaningful vote 3” unless the proposed backstop arrangements for the Irish border are revised, he said.
But Mrs May received a boost from former chancellor Lord Lamont, who urged fellow Brexiteers to focus on the “prize” of leaving the EU and back her deal.
Chairman of the The European Research Group, Jacob Rees-Mogg, has said the only reason to support the prime minister's deal would be if "the alternative was not leaving the European Union."
He told ITV News: "I would prefer to leave now on March 29 without a deal and I think most people in Britain would like that too, to get this over and done with.
"But if the prime minister of her own volition is seeking to keep us in the European Union pretty much indefinitely that would be even worse than her deal."
Downing Street was scrambling for support for the deal – particularly from the Democratic Unionist Party – in the hope of bringing it back before Parliament ahead of an EU summit on Thursday.
But it is thought the Prime Minister could delay the crucial vote for another week unless she is confident of avoiding a third humiliating defeat on the package, which MPs rejected by 230 votes in January and 149 last week.
She has warned that if her deal is not approved, the UK will have to seek a lengthy extension to negotiations, potentially losing Brexit altogether.
But her hopes of rallying Conservative MPs behind her were dealt a blow by a letter to the Telegraph from 23 Leave-backing backbenchers arguing for a no-deal exit.
“’No deal’ will prove to be the precursor to a very good deal indeed,” wrote the Tory MPs, including former ministers Owen Paterson, Sir John Redwood and David Jones.
“Our moral course is clear: it is not our fault that we are confronted by two unacceptable choices, but it will be our fault if we cast a positive vote in favour of either for fear of the other.”
Mr Johnson said Mrs May’s Agreement would leave the UK “in a position of almost unbearable weakness” for subsequent talks on trade, risking transforming the country into “a kind of economic colony of Brussels”.
The backstop arrangement – under which the UK remains in a customs union until both sides agree a trade deal – gives the EU “an indefinite means of blackmail”, said the Brexit figurehead.
“Unless we have some change – and at present, in the immortal phrase, nothing has changed – it is hard to ask anyone who believes in Brexit to change their mind,” he said.
“There is an EU summit this week. It is not too late to get real change to the backstop. It would be absurd to hold the vote before that has even been attempted.”
But Lord Lamont warned that if the Prime Minister’s deal falls, Brexit may never happen.
Writing in the Daily Mail, he said that “history will not understand if it is Conservative MPs who prevent us claiming our self-government”.
Negotiations with the DUP were expected to continue on Monday, although Downing Street said a formal meeting has not been scheduled.
The 10 DUP MPs are viewed by Downing Street as pivotal, not just for the votes they provide but the influence of their stance on Conservative Eurosceptics.
DUP MLA Jim Wells told BBC Radio 4’s Today programme: “We still have a huge difficulty with the backstop, because we see it as a waiting room for constitutional change.
“We could find ourselves locked in there forever in effect, and once you get in you can never get out. We have to have a mechanism where we can escape the backstop.”
Mr Wells said a proposed “gentlemen’s agreement” that any changes to Northern Ireland’s relationship with the EU would be mirrored by the rest of the UK might prove “unenforceable”.
And he denied that the DUP was taking part in a financial “auction” for its support, insisting that “money is not being discussed on the table at the moment”.
Mr Wells estimated that as many as 30 Tory MPs will never vote for Mrs May’s deal, meaning that a third defeat was “inevitable” with or without DUP support.
So far the number of Tories publicly switching positions falls far short of the 75 MPs Mrs May needs to change sides.
Bolton West MP Chris Green told BBC Radio 4’s Westminster Hour: “I want to vote against it because I don’t believe when Parliament defeated it by the biggest margin in the history of Parliament that was because it was in any way a good deal, and the substance of the deal hasn’t changed.”
But he added that a shift in the DUP’s position would have a “big impact” and the implications of rejecting the deal for a third time weighed heavily on him “because it could lead to a general election, and we don’t know how that will pan out”.
As part of the effort to put pressure on Tory hardliners and the DUP, Chancellor Philip Hammond and International Trade Secretary Liam Fox took to the airwaves on Sunday to make clear that the Prime Minister would not chance a third defeat on her deal.
And Security Minister Ben Wallace, a close ally of Mr Johnson who chaired his abortive bid for the leadership in 2016, urged the former foreign secretary and other Tory Brexiteers to back Mrs May’s deal.
“I know Boris very well and I know he’s passionate about leaving the European Union,” Mr Wallace told BBC Radio 4’s Today programme.
“If he is passionate about that, he will recognise that voting for this deal is the way to deliver Brexit and the way to deliver leaving the EU … I strongly urge my colleagues to vote for it.”
Labour leader Jeremy Corbyn was holding a series of meetings with other Westminster leaders including the SNP’s Ian Blackford and Liberal Democrat Sir Vince Cable and influential backbenchers in an effort to find a consensus on a rival Brexit strategy.