The prime minister was ready to jump on a plane to Brussels for discussions as soon as new wording had been approved by the DUP, amid growing anxiety about securing a deal in time for next week’s European council.
Donald Tusk, the president of the European council, and the European commission president, Jean-Claude Juncker, had cleared their schedules for a late meal with May on Thursday night.
However, the prime minister would not commit to travelling until she had a firm agreement nailed down with the DUP, after the party unexpectedly vetoed the first proposal on Monday over fears it would give Northern Ireland a different Brexit deal to the rest of the UK.
As the clock ticked down, Tusk said he would be giving a statement on the situation at 6.50am on Friday – before the stock exchange opened – prompting speculation that he was about to pass on information that could affect the markets.
Sources close to Tusk said he would be leaving early for a meeting in Hungary but there was growing speculation that a new proposal for solving the Irish border issue would be ready on Friday morning.
“Less than a week to go to [the European council], so Tusk will make a situational update of the Brexit situation in that context,” the source said.
A negotiating team from the DUP, including its Westminster leader, Nigel Dodds, spent much of the day holed up in the Cabinet Office with May’s team trying to make headway with a new draft text. Both DUP and No 10 sources said some progress had been made but they were not yet in a position to make an announcement.
Earlier on Thursday, Simon Coveney, the Irish trade minister, indicated that there was still room for compromise but made it clear his side would not budge on the key issue of some regulatory alignment between Northern Ireland and the Irish Republic to prevent the reemergence of a hard border.
“We are in a position where we still need to find a way forward but, let me be very clear, the core issues that Ireland got agreement on at the start of this week are not changing,” he said.
The DUP had objected to the wording because they thought it could result in Northern Ireland getting detached in regulatory terms from the rest of the UK. This was quickly backed by senior Conservative supporters, who warned that Northern Ireland must not get a different regulatory regime from the rest of the country and that there was little point in Brexit if the UK retained the same regulations as the EU.
Boris Johnson, the foreign secretary, fired off a warning shot to the prime minister on Thursday that widespread regulatory alignment between the UK and Brussels was out of the question.
Answering questions after a foreign policy speech in London, Johnson said: “Whatever way we devise for getting on to the body of the talks, it’s got to be consistent with the whole of the United Kingdom taking back control of our laws, of our borders and of our cash,” he said.
“What we want to achieve is a new relationship, a deep and special partnership in which we can intensify our trade links and continue to work together on foreign policy and security.
“But to achieve that we need to get going with the second part of the talks. That’s the exciting bit.”
Adding to the pressure on May, a lobby group linked to the former Vote Leave campaign has warned May that signing up to regulatory alignment with the EU to solve the Irish border problem will not allow Britain to “take back control” from Brussels.
Change Britain, which was launched last year with the backing of Johnson and the environment secretary, Michael Gove, made clear its belief that such a move would fail to respect the mandate of the referendum result.
Gisela Stuart, the former Labour MP who led the Vote Leave campaign alongside Johnson and Gove, said: “[It] would be completely unacceptable if we were forced to agree a deal where regulatory alignment saw the UK continue to be subject to rules designed and imposed by Brussels.
“It would be single market membership in all but name. The government must stand firm in the negotiations and stick to the principles set out in the prime minister’s Lancaster House speech.”
The group said May would be signing up to become a “rule taker” if she accepted regulatory alignment in which the UK would have to comply with rules made in Brussels without having elected representatives to oversee the formation and amendment of those laws.
Change Britain said it was not the same as “mutual recognition” of each other’s laws and regulations, which is a different and clearly defined concept in EU trade policy.
Gove and Johnson are not directly involved in Change Britain but the group’s website carries a video of the foreign secretary endorsing its formation. Gove led its policy commission until he became environment secretary.
Senior Conservatives have been further infuriated by May’s apparent attempt to bounce them into the deal, as she did not consult all her cabinet colleagues or the DUP on the exact wording before pressing ahead.
There is particular worry among Brexit-supporting MPs that May’s No 10 operation has taken too much control over the process to the exclusion of senior leave backers in the cabinet, such as Johnson, Gove, David Davis and Liam Fox.
At the same time, allies of Davis have once again been floating to MPs the idea that he should take over as prime minister – at least as a caretaker leader until the end of Brexit.
However, several newer intake MPs told the Guardian that idea should be given short shrift as the bulk of the party still believes a leadership contest would be a damaging distraction at such a crucial time in the EU negotiations.