Scotland Secretary David Mundell has faced fresh calls from both Labour and SNP MPs to resign. 

During Scottish questions, SNP frontbenchers said Mr Mundell had indicated that a differentiated deal for Northern Ireland and keeping fishermen trapped in the Common Fisheries Policy (CFP) would be matters for resignation.

Pointing out how the backstop deal would lead to both these outcomes, SNP Cabinet Office spokesman Tommy Sheppard asked, "how can he justify remaining in the Cabinet"? 

Mr Sheppard said: "He has publicly refuted the differentiation on which this Withdrawal Agreement is based, he has threatened to resign on numerous occasions.

"Now he has nailed his colours to the Prime Minister's mast and invested what political capital he has left in this deal.

"If the Withdrawal Agreement is rejected by this Parliament, as surely will be the case, will he resign his position?"

Speaking during Scottish questions in the Commons, Mr Mundell said his position was clear.

READ MORE: Nicola Sturgeon says David Mundell should resign   

He said: "The integrity of the UK must be preserved.
"The SNP and Nicola Sturgeon see Brexit as an opportunity to break up the UK, so above all else I put that first."

SNP shadow Commons leader Pete Wishart compared Mr Mundell to a "demented" Grand Old Duke of York.

"I don't know if he realises how ridiculous he has looked with his resignation-non-resignation business," he said.

"He is like a demented Grand Old Duke of York - he's led his merry band of Scotch Tories halfway up resignation hill and then forgotten whether he is going up or down.

"Scotland voted overwhelmingly against Brexit so if he can't represent the people of Scotland will he just resign and get out of the way for goodness sake?"

READ MORE: David Mundell insists 'carpetbaggers' won't force him to resign

Mr Mundell traded insults with the SNP veteran and appeared content to back Mrs May's deal.

Shadow Scotland minister Paul Sweeney said: "The reality is that the secretary of state cannot guarantee that the UK won't be pushed into the backstop indefinitely if access to waters and quota shares are not agreed with the EU.

"That's an undeniable breach of his red line. He promised to resign over that very issue and yet he's still here desperately claiming it's a false choice between the no deal and a bad deal.

"When did they realise that he cared more about his ministerial Merc than a good deal for Scotland's fishermen?"

Mr Mundell replied: "In all these debates on fishing where is Scottish Labour lining up? They are lining up with (French) President Macron to do down this country.

"Our Prime Minister is fighting for the best possible deal for our fishermen."

Ms Laird added: "The secretary of state drew red lines for his support of the Brexit deal on the integrity of the UK and on fishing. Unless those things were protected, he would resign.

"The Prime Minister has come back with a deal that creates a border in the Irish Sea and sells out Scottish fishermen, so can I ask what he is still doing at the Despatch Box?"

Mr Mundell replied: "What I am doing is standing up for the integrity of the UK and when I see Jeremy Corbyn and Nicola Sturgeon caballing about what they are going to do next and no doubt agreeing that the keys of 10 Downing Street will be handed over to Labour for another independence referendum, I know I'm doing the right thing."

He said: "There is no greater expert in this House on being ridiculous than him, swinging one way and another on every issue of the day.

"I'm quite clear, the UK voted to leave the EU and this Government will deliver that."