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.
Mr Cox has dismissed reports he has given up on securing a firm end date 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.
Separately, Scottish and Welsh politicians are joining forces in an attempt to force the prime minister to change her position on Brexit. For the first time since devolution 20 years ago, they will debate the same motion, at the same time.
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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.