Ministers will resume efforts later to secure legally-binding changes to Theresa May’s Brexit deal that might get MPs’ backing in a week’s time.
Brexit Secretary Stephen Barclay and Attorney General Geoffrey Cox will meet EU officials in Brussels in search of guarantees over the backstop plan to avoid border checks in Ireland.
He has dismissed reports he has given up on securing a firm end date or means of exit to ensure the UK is not stuck.
MPs will vote on the deal by 12 March.
The UK is currently scheduled to leave the European Union on 29 March.
If MPs reject the withdrawal agreement for a second time, they will have the opportunity to vote on whether to go ahead in just over three weeks’ time without any kind of negotiated deal.
If they decide against, they will then have a vote on whether to extend negotiations and push the date of departure back by several months.
Leading Brexiteers are hoping Mr Cox will be able to change his legal advice to satisfy them that the backstop – a controversial plan which will see the UK aligned with EU customs rules until the two sides’ future relationship is agreed or alternative arrangements worked out – will not endure indefinitely.
They have set a number of tests for the government’s chief law officer and other ministers ahead of next week’s votes.
Michael Tomlinson, one of an eight-strong “star chamber” of Conservative MPs who will scrutinise what is brought back from Brussels, said only significant changes to the backstop would do.
“We support the prime minister in seeking treaty-level changes,” he said after the group’s first meeting on Monday.
A “proper analysis” of any new text would be needed to allow them to “form a judgement”, he added.
Mr Cox took to Twitter on Monday after newspaper reports suggested he had turned his attention away from the concrete “freedom clause” demanded by many MPs to assurances that the backstop would fall away if talks on a future relationship break down.
Meanwhile, Labour’s Brexit spokesman Sir Keir Starmer has urged his MPs not to weaken in their resolve to oppose the PM’s agreement when it returns to the Commons.
He told a meeting in Westminster “we rejected the deal last time for good reasons and we should do so again”.