Theresa May faces resistance over her request to the European Union for Brexit to be delayed potentially until June 30, with Brussels expected to insist on a longer extension.
The Prime Minister wrote to European Council president Donald Tusk requesting the delay, with an option to leave earlier if she can get a Brexit deal through Parliament.
Mrs May said she will seek to secure ratification of the deal before European elections on May 23, but will make “responsible preparations” for the UK to take part in the polls if that does not prove possible.
But cross-party talks with Labour appear to have stalled, with shadow Brexit secretary Sir Keir Starmer saying it was “disappointing” that Mrs May was refusing to consider changes to the terms of her deal.
But Downing Street insisted that the Government had made “serious proposals” and was “prepared to pursue changes” to the Political Declaration, which sets out the framework for the future relationship with Brussels.
Mrs May’s request for an extension to the Article 50 process will be considered at an emergency EU summit on April 10, where it requires the unanimous agreement of the leaders of the remaining 27 member states.
EU sources said Mr Tusk is recommending a longer postponement of one year, with a break clause in the case of earlier ratification, in a so-called “flextension” deal.
Irish premier Leo Varadkar said a longer delay to Brexit “might make more sense” than the UK seeking “rolling extensions where there is an extension every couple of weeks or every couple of months because that just adds to the uncertainty for citizens, for businesses and for farmers”.
France’s Europe minister Amelie de Montchalin warned that an extension would not be granted automatically.
It would require the UK to put forward a proposal with “clear and credible political backing” and “in the absence of such a plan, we would have to acknowledge that the UK chose to leave the EU in a disorderly manner”.
Prominent Brexiteer Jacob Rees-Mogg suggested the UK should retaliate any long extension by using its continued membership to block moves towards closer EU integration.
“If a long extension leaves us stuck in the EU we should be as difficult as possible,” he tweeted.
“We could veto any increase in the budget, obstruct the putative EU army and block (French President Emmanuel) Macron’s integrationist schemes.”
Mrs May has already obtained one extension to the Article 50 withdrawal process, postponing the date of Brexit from March 29 to April 12 – next Friday.
She was forced to seek a second delay after her deal was rejected for a third time by MPs last week.
In her letter, Mrs May said that if ongoing talks with Labour do not lead to a “single unified approach soon” then the Government would instead look to establish a “consensus” on options on a future relationship that could be put to the Commons.
She wrote: “The Government stands ready to abide by the decision of the House, if the Opposition will commit to doing the same.”
Talks aimed at finding a way out of the Brexit deadlock continued between the Government and Labour negotiating teams on Friday.
Speaking during a visit to south Wales to mark his party’s victory in the Newport West by-election, Jeremy Corbyn said: “There’s been no obvious move on the side of the Government as of yet, we’re continuing those talks.”
He added: “We have to bring an end to this process so there is a degree of security and certainty to people all across Britain.”
Labour’s frustration with the progress of the talks was evident after an exchange of letters with the Government on Friday.
Sir Keir said: “So far, the Government isn’t proposing any changes to the deal. In particular, it’s not countenancing any changes to the actual wording of the Political Declaration.
“Now obviously that’s disappointing; compromise requires change. We want the talks to continue and we’ve written in those terms to the Government, but we do need change if we’re going to compromise.”
A Downing Street spokesman said: “We have made serious proposals in talks this week, and are prepared to pursue changes to the Political Declaration in order to deliver a deal that is acceptable to both sides.
“We are ready to hold further detailed discussions this weekend in order to seek any such changes in the run-up to European Council on Wednesday.
“The Government is determined to work constructively to deliver the Brexit people voted for, and avoid participation in the European parliamentary elections.”
Labour opened nominations on Thursday for candidates to stand in the European elections.
But Foreign Secretary Jeremy Hunt said there was “zero appetite” for the UK to elect MEPs almost three years after voting to leave the EU.