SNP's Westminster leader has questioned how many unsigned letters Boris Johnson has sent since taking over at Downing Street after he added other documents to the Brexit extension request to the EU.

The Prime Minister distanced himself from the legally required document which he sent on Saturday - but refused to sign - while also sending a second note to European Council president Donald Tusk.

Speaking on the BBC's Sunday Politics Scotland programme, Ian Blackford was critical of Johnson's move where he suggested in his other document such an extension would be "deeply corrosive".

However the SNP MP refused to be drawn on any court action this week but did say "there is a clear case that he is in contempt of Parliament" - something shadow chancellor John McDonnell also alluded to during an interview with Sky on Sunday.

Blackford said: "The key letter, the one seeking the extension, seems to be a photocopy of the instruction that he has been given by Parliament and the courts and he's unsigned.

"It really does beg the question how many other unsigned letters has Boris Johnson sent as Prime Minister?

"He's not treating the office of Prime Ministership with any respect or any dignity, it will be a matter for the courts.

"I think there is an issue as to whether or not he's in breach of the court given what happened a couple of weeks ago given what happened when Joanna (Cherry) brought her action, but certainly I think there's an issue about being in contempt of Parliament.

"I think the court also made clear that if the Prime Minister didn't follow the letter of the law then the court would expect him to make a judgment on that so I would strongly suspect you may see action taking place in the court over the course of the coming days.

"We'll take our responsibilities in Parliament and we have got an extraordinary week in front of us. I think there is a clear case that he is in contempt of Parliament in the way he's acting. Others will take their responsibilities through the legal process."

The move followed a special sitting of the Commons where MPs voted by 322 to 306 in favour of an amendment withholding approval of Johnson's Brexit deal until legislation to implement it is in place.

In an interview with Andrew Marr on Sunday shadow Brexit secretary Sir Keir Starmer suggested the possibility Labour could back Johnson's deal if a new national poll was attached to it.

Scottish Labour MP Ian Murray, also speaking on Sunday Politics Scotland, said it has "always been the compromise we've been putting forward".

He added: "The SNP have gone slightly cold on a people's vote. It wasn't mentioned at their conference last week in any of their leader's speeches - including Ian Blackford's - and they didn't use their amendment yesterday to push for a people's vote where we did.

"I don't know what the position of the SNP is on a people's vote at the moment but I would have thought given what they've said in the past that if this amendment comes forward they would support it and I would hope they wholeheartedly support the remain campaign."

Scottish Conservative MP Luke Graham also told the programme: "No deal is what we've been trying to avoid all along.

"What we saw in the last week is the Prime Minister actually deliver a deal that delivers on a lot of the objectives that we were trying to achieve as a country.

"There's less discussion about no deal, it's a discussion about we've got a deal, the EU have agreed it, it's now for us to agree it as well.

"The Prime Minister has written his letters in accordance with the law and now we're focusing on getting a deal.

"We've got one on the table and it's time for MPs right across the House of Commons to come together and actually vote for that deal so we can move forward."