Boris Johnson has been accused of "childish manoeuvres" after sending two letters to European leaders - one requesting a Brexit delay and another opposing a delay.

The Prime Minister was legally obliged under the so-called Benn Act to request an Article 50 extension from the EU until the end of January.

The move was forced on him after he failed to secure Commons approval for his new Brexit deal by the October 19 deadline.

Johnson ordered a senior diplomat to send an unsigned letter requesting the delay, then sent a second note to European Council president Donald Tusk stressing he was only doing parliament's bidding.

In the second letter, the PM said a Brexit extension would be "deeply corrosive" and emphasised that his government supports leaving the EU on October 31 with no further delay.

He wrote to Tusk on Saturday: "When I spoke in parliament this morning, I noted the corrosive impact of the long delay in delivering the mandate of the British people from the 2016 referendum.

"I made clear that, while I believe passionately that both the UK and the EU will benefit from our decision to withdraw and develop a new relationship, that relationship will be founded on our deep respect and affection for our shared culture, civilisation, values and interests.

"We will remain the EU's closest partner and friend. The deal we approved at last week's European Council is a good deal for the whole of the UK and the whole of the EU.

"Regrettably, parliament missed the opportunity to inject momentum into the ratification process for the new withdrawal agreement."

Johnson went on: "The UK parliament representative will therefore submit the request mandated by the EU (Withdrawal) (No.2) Act 2019 later today.

"It is, of course, for the European Council to decide when to consider the request and whether to grant it.

The European Council president acknowledged receipt of the Brexit delay request and made no mention of the Prime Minister's second note.

Tusk tweeted: "The extension request has just arrived. I will now start consulting EU leaders on how to react."

Opposition parties have suggested Johnson is trying to circumvent the the law and could end up in court over the move.

SNP Westminster leader Ian Blackford said: "After being defeated on his extreme Brexit deal earlier, Boris Johnson is now attempting to scheme his way out of due process with childish manoeuvres.

"This is a Tory leader that is simply unfit for the office he holds.

"Boris Johnson is not above the law and if he does not fully abide by the Benn Act and secure an extension then we will see him in court.

"He has given the court an undertaking that he will not frustrate the purpose of the Benn Act - his latest antics suggest that is exactly what he intends to do."

Johnson had hoped to get backing for his Brexit deal at a special Saturday sitting of MPs.

But the Commons voted by 322 to 306 in favour of an amendment withholding approval of his Brexit deal until legislation to implement it is in place.

A defiant Prime Minister told MPs he would not negotiate a Brexit extension and later rang European leaders to say the delay request "is parliament's letter, not my letter".