A deadline of around 2021 is being mooted, which would ensure the unpopular Irish “backstop” plan lasted no longer than a year.
No 10’s focus has changed, however, from fixing a date for the backstop to end, to setting a date for the future partnership which would make it redundant.
But this was dismissed as impossible to meet by a former head of the Treasury. Lord Macpherson said in a tweet: “Time for some honesty about Brexit.
“There is no way the UK will negotiate a trade deal with the EU by December 2020.” He said even 2022 was “very optimistic” and a deal would probably take until the middle of the next decade.
Downing Street said Mrs May spoke over the Christmas break with Jean-Claude Juncker, Emmanuel Macron, Angela Merkel and Mark Rutte in a bid to get a concession on the backstop to reduce a giant Tory rebellion.
Senior ministers say Irish premier Leo Varadkar is blocking Theresa May’s appeal for 11th-hour concessions on the backstop because he does not realise how close Britain is to crashing out of the EU without a deal.
“The Irish think that we will cave in at the last minute,” a senior minister said. “The real question is when the Irish start to think that no deal could actually become reality.”
Mr Varadkar is now the focus of efforts at EU level to broker reassurances that might persuade enough Conservative MPs to peel off from a giant rebellion against the withdrawal agreement when it goes to a meaningful vote in the Commons on January 15.
German foreign minister Heiko Maas will visit Dublin tomorrow for talks, following a 40-minute conversation over the phone last week between the taoiseach and Angela Merkel. The German chancellor intervened after she was contacted by Mrs May twice over Christmas.
But Mr Varadkar has stated he is not considering changes to the agreement and British ministers fear it will take a resounding defeat for the withdrawal agreement before Ireland is willing to consider serious concessions.
The backstop would see Northern Ireland remain aligned to some rules of the EU single market, if another solution is not found before the end of the transition period in December 2020.
Mrs May is threatening to cancel MPs’ weekends and even their half-term break to get critical Brexit legislation through Parliament.
Her spokesman said she would do “whatever is required” to pass laws needed to keep the country running after the withdrawal date of March 29.
As well as the deal, MPs need to pass a Trade Bill, Agriculture Bill, Fisheries Bill, Healthcare Bill, Immigration Bill and a Financial services Bill.