Theresa May will meet with senior ministers later in an attempt to resolve tensions over the government’s Brexit “backstop” plan.
In the proposal the UK would match EU tariffs temporarily in order to avoid a hard Irish border post-Brexit.
Number 10 had been expected to publish the “temporary customs arrangement” on Thursday, but faced resistance from Brexit Secretary David Davis.
Its publication could now be delayed until the end of the week.
The proposal will outline what would happen should no permanent solution be agreed with the EU before the UK’s 2019 exit – but it might not specify an end date.
BBC political editor Laura Kuenssberg said Downing Street believed it had enough support from senior ministers to publish the proposal.
“But what they hadn’t quite bargained for was the level of resistance from the man who is meant to be in charge of this process (Mr Davis),” who wants a time limit added to the backstop, she added.
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Mr Davis told a press conference on Wednesday that he “expected” there to be a time limit in the signed-off version of the plan.
Speaking in London, he said the details had yet to be approved and that he believed Thursday’s meeting of the cabinet’s Brexit sub-committee would be “decisive”.
Number 10 says it does not believe the contingency plan will ever come into effect because a customs arrangement – seen as vital to preventing a hard border between Northern Ireland and the Republic of Ireland – would be agreed as part of the overall withdrawal deal.
But proposals would include a time limit, Downing Street has said.
By Laura Kuenssberg, BBC News political editor
No 10 have prepared a proposal for a “Temporary Customs Arrangement”, where the UK would retain close ties to the EU for an indeterminate period after the end of the transition period – past 2020 – in case none of their hoped for customs fixes come to pass.
They believed they had the support of senior ministers to publish it on Thursday, even without explicit and detailed discussions of the written paper itself in the inner Brexit cabinet, let alone the full gathering of senior ministers.
It became clear, however, and rather surprisingly to the outside observer, that the man in government who is meant to be in charge of the Brexit process was not completely on-board.
So the brakes have been slammed on publishing the paper until meetings and discussions between senior ministers on Thursday.
Sources in Brussels have told BBC Europe editor Katya Adler that Mr Davis will go to Brussels on Monday after requesting an “informal” meeting with his EU counterpart, Michael Barnier.
The UK has said it will leave the EU’s customs union but has yet to agree on what will replace it.
The UK has said that the EU’s proposed option – keeping Northern Ireland in the customs union – would effectively create a border between Northern Ireland and the rest of the UK and was not acceptable.
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Your guide to Brexit jargon
Instead, the UK is proposing a “backstop” option which will see the UK temporarily aligned with the EU’s customs union after December 2020 – when the 21-month post-Brexit transition period ends.
The plan, which Theresa May has said would only apply in a “limited set of circumstances”, would see the UK match EU tariffs in order to avoid border checks and allow it to sign and implement its own trade deals.
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The BBC understands the plan circulated among some ministers on Wednesday morning refers explicitly to the whole of the UK rather than just to Northern Ireland.
Pressed on the issue at Prime Minister’s Questions, Theresa May insisted the UK was on track to leave the EU in March 2019 and that the transition period would last no longer than 31 December 2020.
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