Boris Johnson will ask the EU for a Brexit delay if no deal has been agreed by October 19, despite his insistence he would rather "die in a ditch", according to court papers.
The so-called Benn Act was passed by Westminster last month requiring the Government to ask for an extension until January 31 if an agreement is not reached with the EU by October 19.
But the PM, while promising to abide by the legislation, has said Britain would leave the EU, "do or die", on Oct. 31.
In submissions to Scotland's Highest Court, where anti-Brexit campaigners are seeking to gain an order to force him to comply with the law, the government said that Johnson accepted that he was obliged to send a letter to the EU asking for a delay.
The legal action - led by businessman Vince Dale, SNP MP Joanna Cherry QC and Jolyon Maugham QC - will ask the court to require Mr Johnson to seek an extension to avoid leaving the EU without a deal.
Aidan O'Neill QC, who is representing the trio, told the court that submissions from the government revealed the prime minister "will send a letter... no later than 19 October" to the EU.
The bombshell documents come after the prime minister used his Tory conference speech on Wednesday to promise to "get Brexit done" by exit day, come what may.
He told delegates: "That is why we are coming out of the EU on October 31, come what may conference.
"Let’s get Brexit done. We can we must and we will, even though things have not been made easier by the surrender bill."
In an earlier statement, Ms Cherry said: "Like much of what Boris Johnson says, there is a gulf of truth between the obvious facts of the matter and what he and his Government have been saying.
"He cannot be trusted, and this court action is about ensuring he abides by the law.
"If Boris Johnson tries to defy the law and defy both the Holyrood and Westminster parliaments by crashing out of the EU without a deal - then we are calling on the Scottish courts to uphold the law."
Speaking to BBC Radio Scotland's Good Morning Scotland programme on Friday, she added: "We're not bringing this case because we think there's any loophole in the Benn Act.
"We're bringing this case because we're dealing with a British Prime Minister who brags about not obeying the law and has form for doing things that are unlawful.
"Boris Johnson is not above the law, whether in Scotland or south of the border, thanks to the decision of the UK Supreme Court."
The SNP MP also said she hopes the Prime Minister will be clear on his position about obeying the Benn Act.
She said: "If this court case achieves nothing else but getting him to be clear about what his position is, then it will have achieved something."
Ms Cherry previously won a Supreme Court case against the Government which found the planned prorogation of Parliament until October 14 was unlawful.
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