Boris Johnson will write a letter to the EU asking for a delay to Brexit beyond 31 October if he fails to get an exit deal approved by parliament by Saturday, the Brexit secretary has confirmed.
Stephen Barclay told a committee of MPs that the prime minister will "comply" with legislation, aimed at blocking a no-deal Brexit at the end of the month, passed by opposition MPs last month.
This law, the Benn Act, compels Mr Johnson to ask for a three-month extension to the Article 50 negotiating period to 31 January 2020 if MPs have not approved a Brexit deal - or explicitly authorised a no-deal Brexit - by 19 October.
Earlier this month, it was revealed government documents submitted to a court stated the prime minister "will send a letter... no later than 19 October" to the EU asking for a Brexit delay.
Mr Johnson has repeatedly promised to take the UK out of the EU on 31 October, with or without a deal, and would "rather be dead in a ditch" than ask Brussels for a delay.
Mr Barclay told the House of Commons' Brexit committee on Wednesday: "I can confirm, as the prime minister has repeatedly set out, that firstly the government will comply with the law.
"And, secondly, the government will comply with undertakings given to the court in respect of the law."
Pressed by the committee chair, Labour MP Hilary Benn, as to whether this will involve Mr Johnson sending a letter to the EU, Mr Barclay replied: "I confirm the government will abide by what it set out in that letter."
Asked again if that meant the prime minister sending a letter, Mr Barclay added: "You read it out and I refer back to that text."
Mr Benn, who introduced the so-called "Benn Bill" that led to the legal requirements for a Brexit delay in the absence of a deal, replied: "That's helpful that you have confirmed that he will send that letter."
Mr Barclay later told MPs he is "not aware of any such plan" to send two letters to the EU, following suggestions the prime minister could send one letter asking for a Brexit delay - in order to abide by the law - and another arguing against one.
Mr Barclay said: "We're committed to leaving on 31 October. We think the best way of doing that is with a deal, to leave in a smooth and orderly way.
"That is why the team are, as we speak, involved in intensive negotiations.
"We think there's a political will on both sides to do that. And this is the best way, in our view, of meeting the legislation requirements that you set out."
He also confirmed the government had submitted draft texts on a revised political declaration - the part of the Brexit deal that relates to the future UK-EU relationship - to the bloc's negotiators.
This afternoon, EU chief Brexit negotiator Michel Barnier is due to meet EU diplomats where he will tell them whether or not he can recommend a UK withdrawal agreement, ahead of tomorrow's European Council summit of EU leaders.
Ahead of the Brussels gathering, which Mr Johnson will attend, French President Emmanuel Macron and German Chancellor Angela Merkel will meet in Toulouse.
If a Brexit deal is approved by EU leaders at this week's summit, the House of Commons could be asked to approve an agreement in a rare Saturday sitting.
However, Mr Barclay told the committee he could not yet confirm whether MPs will be asked to be in Westminster this weekend.
EU and UK negotiators are still locked in talks in Brussels over a new Brexit deal, with discussions having run late in to Tuesday night.
Despite talks resuming early the next day, a government source has told Sky News no Brexit deal is expected on Wednesday.
Mr Johnson held a "constructive" telephone call with Irish prime minister Leo Varadkar on Wednesday morning, Downing Street revealed.
The prime minister's spokesman said "progress was made" on a Brexit deal "but there is still work to do".
Mr Johnson told his cabinet that "there was a chance of securing a good deal but we are not there yet and there remain outstanding issues", his official spokesman said.
"Following a positive discussion, cabinet gave the PM its full support in the government's continuing efforts to secure a deal ahead of European Council," he added.
The PM also briefly addressed a meeting of the 1922 committee, with one MP describing Mr Johnson's appearance as "optimistic and upbeat".