This puts him in all-out conflict with MPs, who have ordered him to ask EU leaders for a three-month Brexit delay, under the terms of the Benn Act they forced on him.
On the advice of his Attorney General, Geoffrey Cox, Johnson believes he will be complying - in a narrow sense - with the terms of the Benn Act when his EU ambassador Sir Tim Barrow hands an unsigned photocopy of the pro forma letter contained in the Benn Act to the EU President, Donald Tusk.
Barrow will also hand over a covering letter that says the PM is complying with Parliament's wishes in conveying the unsigned letter, but the clear message will be that Johnson does not want any Brexit delay.
There is a THIRD letter, which Johnson is sending to all 27 EU leaders.
In it the prime minister says that any Brexit delay would be "deeply corrosive", and that postponing the date of leaving the EU would "damage the interests of the UK and our EU partners".
He will urge the EU to continue its own processes to ratify the deal, as will the UK.
Johnson will as soon as Monday, in Scotland’s Court of Session, face his first legal challenge to his refusal to sign the postponement letter.
That court is due to consider whether he is complying with the Benn Act, in a case brought by the SNP’s Joanna Cherry.
As I understand it, if MPs challenge the PM’s decision to say the delay is being requested by Parliament but not by the Government, Johnson is prepared to fight them all the way to the Supreme Court.
According to a senior Downing Street source, the PM is today telephoning EU leaders urging them to make it clear that they do not want a Brexit postponement.
The prime minister believes a number of EU leaders, including France's President Emmanuel Macron and Ireland's Taoiseach Leo Varadkar, may be prepared to make further public statements cautioning against any delay beyond October 31.
ITV News Political Editor Robert Peston explains the ramifications of the PM openly pitting himself against his own Parliament to EU leaders
In a conversation tonight with Macron, the French president reportedly agreed with Johnson that "delay is bad for everyone", said a Downing Street source.
It is thought that the EU will shelve any formal decision on whether to give a Brexit delay, perhaps till an emergency meeting of the European Council that could take place on October 28.
Johnson is obliged to send a letter requesting a Brexit delay, under the terms of the Benn Act, because he failed to secure MPs' approval for his Brexit deal.
That happened when MPs instead voted for Sir Oliver Letwin's amendment to the government's own motion, whose effect is to defer Brexit approval till the relevant associated legislation, the Withdrawal Agreement Bill, goes on the statute book.
Johnson remains confident he will obtain his version of Brexit by October 31.
On Monday he will have a second go at obtaining a meaningful vote in favour of his deal, though it is thought Speaker John Bercow will block him from doing this.
However on Tuesday he will hold a vote on the second reading of the Withdrawal Agreement Bill - it is thought he could narrowly win this.
If he does win that vote, it will be the first proof there is now a path to Parliament approving his - or any - Brexit deal.