THE SNP leadership’s call for David Mundell to resign over the Con-DUP deal has been dismissed as a “silly stunt” by Whitehall insiders, who said it was aimed at distracting attention away from Nicola Sturgeon’s troubles at Holyrood.

The row flared up after the Scottish Government insisted that under the principles of fair funding the £1 billion heading to Northern Ireland under the deal meant that £2.9bn should come to Scotland.

However, the UK Government has insisted the Tory agreement with the Democratic Unionists is outwith the Treasury procedure known as the Barnett Formula, in which departmental spending increases or reductions for England are replicated in Scotland, Wales and Northern Ireland based on a population share.

The SNP seized on comments last week by the Scottish secretary, made ahead of the Con-DUP deal, in which he said "any funding that goes to Northern Ireland, then Barnett rules will ensure appropriate funding comes to Scotland".

At Prime Minister’s Questions, Ian Blackford, the SNP leader, asked Theresa May whether or not she had, therefore, received "any representations from her Scottish secretary about the DUP deal either before or after it was signed".

The PM stressed how because of Barnett Formula consequentials, based on increased spending in England through last year’s Autumn Statement and the Budget, Scotland would be better off to the tune of almost £1.2 billion.

“I do not remember, when that money for Scotland was announced, the honourable gentleman complaining that more money should be going to Northern Ireland. But then of course, he is a Nationalist and not a Unionist,” declared Mrs May.

However, Mr Blackford said the PM had failed to "give a straight answer" and asked the question again.

Mrs May replied: "I can assure him that I regularly receive representations from the Secretary of State for Scotland about matters relating to Scotland, including regular representations which point out that if the Scottish Nationalists actually have the interests of Scotland at heart they will want to remain part of the United Kingdom."

Later, Mr Blackford claimed: “It’s become apparent David Mundell failed to lift a finger to secure any more cash for Scotland through Barnett consequentials; his position is now utterly untenable.

“Either the Scottish secretary has gone back on his word or the new Scottish Tory MPs have been utterly humiliated just days after their election.”

The Highland MP added: “There is absolutely no way that David Mundell can credibly claim to be standing up for Scotland’s interests in the Cabinet and his failure to secure anything for the people of Scotland must now mean he cannot remain in his position.

“The question now is who will last longer; May or Mundell?’’

But a senior UK Government source hit back, saying: “This is a bit of political argy-bargy by the SNP based on a flimsy and silly misrepresentation of what the secretary of state said.

“You don’t need to be a political Einstein to know what’s going on here; it’s a pile of noise meant to distract from Nicola Sturgeon’s difficulties over indyref2 at Holyrood.”

The source stressed how the £1bn promised in the Con-DUP deal was not within the scope of the Barnett Formula and the SNP knew that. He explained that this was all Mr Mundell was saying last week when he made his comments; that the process had to be transparent and the Barnett Formula rules observed; which had been the case.

But when asked if the secretary of state had spoken to the PM about any concerns he might have had in this regard, the source said: “We’re not getting into a blow by blow account of what was said inside Cabinet. The secretary of state constantly makes representations about Scotland; that’s his job.”

He added: “I suspect Ian Blackford is under a lot of pressure to throw a smokescreen around Nicola Sturgeon's difficulties at Holyrood. But it's desperate stuff. Angus Robertson would not have embarrassed his party in this way."