A crucial cabinet meeting to agree the UK’s Brexit negotiating position has been pushed back from Thursday to the weekend or early next week amid a row over whether to provide the full legal advice on the backstop to senior ministers.

Some ministers had believed the cabinet could have met late on Thursday afternoon to sign off Theresa May’s Brexit plan but No 10 indicated that the crunch meeting would not now take place on Thursday or Friday.

Downing Street insisted late on Wednesday that the meeting had not been delayed, although ministers abroad such as Greg Clark, the business secretary who is in Japan, and Sajid Javid, the home secretary who is in Seattle, were ready to fly back at short notice.

Brexiters in the cabinet have been keen to see the entire legal advice, particularly if they were to sign up to a customs backstop to avoid a hard border in Ireland that could only be ended by mutual agreement with the European Union at the crunch meeting.

One cabinet source said the prime minister had indicated at Tuesday’s cabinet meeting that only a summary of the legal advice – underpinning the final backstop proposal – would be made available to its members.

The source said that Michael Gove challenged her and demanded the full legal advice be provided to ministers, prompting concern in Downing Street as to how to respond.

The ministerial code makes clear that where legal advice was attached to cabinet papers “the conclusions may if necessary be summarised but, if this is done, the complete text of the advice should be attached”.

Geoffrey Cox, the attorney general, told colleagues at Tuesday’s cabinet meeting that if the UK were to insist on trying to secure a unilateral exit to the customs backstop, it increased the risk of a no-deal Brexit because the EU did not want to agree to it.

His opinion has been deemed crucial if the government was to justify agreeing that the backstop could only be terminated jointly by the UK and EU, because several ministers – including Javid; the foreign secretary, Jeremy Hunt; and the Brexit secretary, Dominic Raab – have argued it should be capable of being terminated only by the UK.

Meanwhile, Labour, the Liberal Democrats and May’s Northern Irish allies in parliament, the Democratic Unionist party, went further and demanded the normal confidential opinion on the backstop be made public.

Sir Keir Starmer, the shadow Brexit secretary, said the advice must be released to MPs so they could scrutinise the document. He said any backstop agreement had to be robust, meaning it was “essential MPs are given the opportunity to scrutinise the attorney general’s legal advice before voting on the final deal”.

Labour’s aim would be for the advice to be available to MPs, as happened with the Brexit impact assessments. They were made available after Labour forced their release through a humble address motion.

This, or an amendment to a bill, remain options for extracting the legal advice, but it was understood Labour wanted to first await the government’s response. The party has an opposition day debate on Tuesday that would allow it to lay down a humble address.

Tom Brake, the Lib Dems’ Brexit spokesman, said: “Refusing to publish legal advice on Brexit makes a mockery of the discredited mantra ‘take back control’,” while the DUP’s Jeffrey Donaldson said:“It’s in the public interest that we understand fully what is happening here.”

Downing Street has said there was a longstanding convention that the government did not discuss legal advice, “or the existence thereof”.

May will travel to Brussels on Thursday night for a dinner with Nato leaders arranged by Jens Stoltenberg, the organisations secretary general. On Friday, she will attend first world war commemorations in Belgium and France, and have a working lunch with the French president, Emmanuel Macron.

Cabinet ministers who visited the Cabinet Office were also allowed to see a copy of the withdrawal agreement, which is the draft treaty that sets out the terms of the UK’s exit from the EU.

However, Downing Street said the document only contained the 95% that has already been agreed with the EU and that it did not contain any all-important text relating to the Irish border backstop.

A backstop has been deemed necessary to ensure there was no return to a hard border in Ireland if the UK and the EU were unable to secure a long-term free trade deal after the end of the Brexit transition period in 2020.

Both the UK and EU have indicated that they would accept the whole of the UK temporarily staying in the customs union as part of the backstop – leaving only one outstanding question: the mechanism by which the backstop could be brought to an end. Brexiter Tories fear that without a clear exit, it could be used to keep the UK in a customs union permanently.

Earlier, May spoke to Donald Tusk, the president of the EU council, but neither side would comment on what was discussed. Tusk had tweeted that he had been seeking “to take stock of progress in [the Brexit] talks and discuss way ahead”.

EU sources in Brussels were deeply sceptical to the notion that the negotiations were on the brink of a breakthrough. One senior official said that it would be a mistake to “underestimate the incompatibility of the views” of the two negotiating teams on how an all-UK customs union could work as a backstop solution in the withdrawal agreement.

The EU wants reasonable commitments from the UK over regulation and would seek assurances on the access of European fleet to British seas before it has agreed to any such customs arrangement.

But the major decision in London was whether it could accept what EU officials have said privately would be essentially an open-ended customs union with the bloc, with only a “review not exit” clause in the final treaty.