NICOLA Sturgeon should sue the UK Government over its £1 billion deal with the DUP to keep the Tories in power, a senior SNP politician has said.

Former SNP cabinet minister Alex Neil said that legal action could bring down Theresa May and “show how rotten the Union is under the Tories”.

Neil said the deal breaches the Barnett formula, which decides how to fairly share out money across the UK's devolved governments.

He said Sturgeon should instruct her law officers to sue because Scotland receives nothing while Northern Ireland get £1bn in exchange for DUP MPs propping up May in crucial Westminster votes.

Neil added that winning a court battle against the Tories would be "a tremendous blow for freedom" for Scotland.

The former health secretary made the dramatic intervention in this week's Sunday Herald People Behind The Power interview.

Neil said the justification for a legal challenge was because Scotland was disadvantaged by the Tory-DUP funding arrangement.

However, he added that overturning a deal he claimed had "betrayed the people of Scotland" would boost the campaign for independence.

SNP ministers have threatened a formal dispute over the deal – which they say should have meant Scotland getting £2.9bn if the money was spread out proportionally.

But he said launching that process at the UK's Joint Ministerial Committee would take too long. In his view, the Tory-DUP deal had "done us out of £2.9bn" and the best option was to sue Westminster ministers for the cash.

Neil said the Tories had "sold us down the river" by breaching the Barnett formula's "fiscal framework" on ensuring funds are shared fairly between the four nations of the UK.

Speaking about a formal dispute, he said: “That takes time I think there's a quicker way to pursue it through the courts.

"I think they have breached a fundamental part of the financial settlement and I think they have breached the principles of the fiscal framework.

"If we won that legal case I think it would force Theresa May out of Downing Street.

"What a tremendous blow for freedom that would be.

"It would show how rotten the Union is under the Tories.”

Neil said he did not begrudge Northern Ireland the £1bn, but said that Scotland should have £2.9bn in extra funding.

Labour has said that there should be £1.67bn for Wales if the money was spread out proportionally.

Neil said: "To sue them for the £2.9bn, even if it's not successful, would show how rotten this deal is for Scotland and how the Tories have sold us down the river.

"They've broken the Barnett formula and have betrayed the people of Scotland. They have done us out of £2.9bn."

When asked if successfully suing the UK Government would boost the independence campaign, Neil said: "It could, but that's not the reason for doing it as we need that money."

In response, the SNP Government said Scotland was facing a cut to its funding from Westminster as a consequence of the Tories's £1bn deal with the DUP.

The Scottish Government said that a letter from the Chief Secretary to the Treasury Liz Truss to Scotland's finance secretary Derek Mackay showed the deal has put funding for public for services elsewhere at risk.

Truss states that “there has been no change in UK Government Departmental Expenditure Limits” (DEL) as a consequence of the arrangement.

The Scottish Government said the Tory minister's admission means funding could be cut from other areas to pay for the deal with the DUP.

A Scottish Government source: “It is a smoking gun which reveals that other government departments face cuts to pay for the cash for votes deal that was struck – and that would see Scotland’s funding reduced too."

In response to Neil, a UK Government spokeswoman said: "The UK Government has the power to provide funding outside Barnett - such as investing nearly £700 million in UK City Deals in Scotland."