Boris Johnson will send a letter to the EU by 00:00 BST to request a Brexit delay – but he will not sign it, according to a Downing Street source.
The request will be accompanied by a second letter, signed by Mr Johnson, which will say he believes that a delay would be a mistake, the source said.
The PM was required by law to ask the EU for an extension to the 31 October deadline after losing a Commons vote.
It is expected Donald Tusk will now consult EU leaders about an extension.
The first letter from Downing Street to Mr Tusk, EU Council President, requests a delay to the Brexit process, to comply with the so-called Benn Act, passed last month by MPs.
A hard copy and email copy of the letter will be conveyed by Sir Tim Barrow, the UK’s representative in Brussels.
But according to the senior Number 10 source, the prime minister will not sign the letter to Mr Tusk and it will be accompanied by two additional documents.
The first will be a cover note from Sir Tim, explaining that the letter complies with the law as agreed by Parliament.
But there will also be a second letter from Mr Johnson – signed off this time – which will make clear that he believes that a delay would be a mistake
It will also appeal to EU leaders to ask MPs to reconsider their decision, and vote for the deal the UK and EU have agreed without any further delays.
Setback for PM
At a special sitting in the Commons on Saturday, MPs voted in favour of an amendment withholding approval of Mr Johnson’s Brexit deal until legislation to implement it is in place.
Tabled by Tory MP Sir Oliver Letwin, the amendment was intended to ensure that Mr Johnson would comply with the terms of the so-called Benn Act.
Under that Act, which required the PM to seek a Brexit extension, Mr Johnson had until 23:00 BST on Saturday to send a letter requesting an extension.
In a letter to MPs and peers on Saturday evening, he warned that the EU could reject “Parliament’s request for further delay” and added that he “will not negotiate a delay”.
“I will tell the EU what I have told the British public for my 88 days as prime minister: further delay is not a solution,” he said.
The Commons defeat marked a major setback for the PM, who has repeatedly insisted that the UK will leave at the end of the month come what may.
Mr Johnson told the Commons that he was not “daunted or dismayed” by the defeat and remained committed to taking Britain out by the end of the month on the basis of his “excellent deal”.
An EU source said that once Mr Tusk received the letter, he would start consulting EU leaders on how to react – which may take a few days, BBC Brussels reporter Adam Fleming reported.
Mr Johnson has vowed to bring in legislation on Monday to implement the deal he struck with Brussels this week.
MPs could also be given another vote on the deal then, if Commons Speaker John Bercow allows it.
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