THE Scottish Tories were yesterday accused of having “zero” influence on the Westminster government after it struck a “back door” deal with the DUP that gives an extra £1 billion to Northern Ireland.

Nicola Sturgeon launched the attack, warning that by “ignoring” the Barnett formula through which Treasury funding is delivered to the devolved governments, Scotland had missed out on £2.9bn.

The furious row broke out after the terms agreed by the DUP in return for propping up Theresa May’s minority government were announced following more than two weeks of negotiations.

The agreement came a day after Scottish Secretary David Mundell said he would not “support funding which deliberately sought to subvert the Barnett rules” and weeks after Ruth Davidson boasted of the influence her 13 MPs would have.

A furious Sturgeon tweeted: “Any sense of fairness sacrificed on the altar of grubby DUP deal to let PM cling to power, & Scots Tories influence in No10 shown to be zero”.

In a statement, Sturgeon said described the deal as “grubby” and “shameless” and said it revealed the Tories would stop at nothing to hold on to power and were prepared to “sacrifice” the basic principles of devolution.

“By ignoring the Barnett formula, Scotland will be missing out on an estimated £2.9bn in funding for our public services – that is the price to Scottish taxpayers for the Tories to stay in power,” she said.

“This breaks the very principles that underpin devolution and the funding settlement the Tories pledged to protect... This is the worst kind of pork-barrel politics, which has shredded the last vestiges of credibility of this weakened Prime Minister.”

The First Minister went on to underline Mundell’s comments on Sunday, arguing that “instead of fighting Scotland’s corner [he] appears to have just surrendered”.

“He and Ruth Davidson should now live up to their boasts by preventing this deal going through – they should order Scottish Tory MPs to use their votes to put a halt to it,” Sturgeon added.

“This total disregard of the principles of devolution will haunt the Tories for years to come. In government and at Westminster the SNP will continue to pursue the UK Government for a fair deal for Scotland.”

The SNP’s Westminster leader Ian Blackford also attacked Mundell’s position, saying: “Only 24 hours ago David Mundell was categorically assuring us that Scotland would be in line for Barnett consequentials as a result of the DUP deal – so he has seemingly either been deliberately misleading people or he is completely out of the loop even in Theresa May’s crumbling government.”

Patrick Harvie, co-convener of the Scottish Greens, who has previously attacked the prospect of a Tory deal with the DUP over the latter’s opposition to equal marriage and climate change, said Mundell’s position was untenable.

“David Mundell has been crystal clear that he would not back this kind of deal,” he said.

“It is impossible to see how he can continue as Secretary of State for Scotland, and if he doesn’t resign in response to this shameless deal with the homophobes and climate deniers of the DUP, nobody in Scotland can ever believe a word he says again.”

Scottish Labour leader Kezia Dugdale also called on Ruth Davidson and her new Scottish MPs to demand “extra cash to reverse the spending cuts her government has inflicted on Scotland”.

“This deal with the DUP has taken more than two weeks to stitch up, proving just how little authority Theresa May has left,” she said.

“If the price of propping up this miserable Tory government is hundreds of millions of pounds for Northern Ireland, it is vital that all nations and regions of the UK also get extra funding to end austerity.

“If Scottish Tory leader Ruth Davidson has any influence in Downing Street at all, she will be demanding extra cash to reverse the spending cuts her government has inflicted on Scotland.”

Davidson attempted to defend the extra money to the Northern Ireland Executive, suggesting it was similar to funding Scotland had received through the city deal scheme.

“The Barnett formula ensures that if funding for public services goes up in England, it also does across the devolved nations if they are responsible for delivering these services. That system remains in place,” she said. “But the UK Government has always been able to spend outside Barnett – like the city deals, which invested £500 million directly in Glasgow, £125m in Aberdeen and £53m in Inverness.

“Or like the £5m for the V&A Dundee, the £5m for the Glasgow School of Art or £5m on regenerating Helensburgh’s waterfront.

“With its distinct politics, Northern Ireland has received this sort of special funding package before – the last one in 2015.

“It’s absurd for the SNP to criticise UK Government spending on top of Barnett in Northern Ireland when the exact same thing happens in Scotland.”

As part of the pact, the DUP insisted triple lock protections of pensions and winter fuel payments will remain.

In the Commons, DUP deputy leader Nigel Dodds slammed “outrage” from opponents as “hypocrisy of the highest order” saying his party may publish correspondence with Labour and SNP in previous elections.