ALEX Salmond has warned Tory ministers that a failure to respect a Holyrood vote against Brexit would lead to a second independence referendum. Salmond told the Sunday Herald that Westminster "can either respect the wishes of Scottish people or face indyref2", as the SNP's Brexit war with Theresa May's government intensified.

The dramatic intervention followed a landmark court case on whether MPs can vote on leaving the EU before Article 50, the formal process of leaving the EU, can be invoked.

Scotland's top law officer James Wolffe warned that not consulting the Scottish Parliament on Brexit would "bypass an important constitutional requirement", at the end of a four-day Supreme Court hearing in London on Thursday.

Now former First Minister Salmond has said Holyrood voting against Brexit would "pile the pressure" on the Prime Minister to accept Sturgeon's flagship demand for Scotland to retain its place in the single market.

Sturgeon will unveil specific Scottish Government proposals in the next fortnight to keep Scotland in the territory that allows for the free movement of goods and services.

Salmond said that the First Minister's paper will give "guidance and strategy" in the SNP's battle with the Tory government during the Brexit process. However, he added that Holyrood voting against Brexit would give Sturgeon a "very powerful hand" in seeking to protect Scotland's place in the single market.

Salmond, the SNP's international affairs spokesperson at Westminster, said: "It would pile pressure on the UK Government to make some specific concession with regard to the single market. It would give a very powerful hand to Nicola Sturgeon over Scotland's position."

Salmond, speaking about Wolffe's legal argument that the Scottish Parliament needs to be consulted before the UK can begin the formal process of leaving the EU, said: "The Lord Advocate's arguments were a class above."

A judgement from the Supreme Court is expected to be delivered in January.

The UK government has said that it does not believe it is necessary to ask either the UK or Scottish Parliaments, and wants to trigger Article 50 by using existing ministerial powers – the royal prerogative.

SNP ministers have made the case that Holyrood should be formally consulted on Brexit and have asked for the parliament's consent. However, Salmond said that if Westminster ignored Holyrood's wishes and insisted on retaining ultimate authority it would set a clear path towards a second independence referendum.

He said: "If the UK Government doesn't accede to Scotland's interests and it ignores the Scottish Parliament then that makes another independence referendum as the First Minister has already said highly likely. If the UK Government fails to respect the wishes of the Scottish people, it creates the case for indyref2.

"The UK Government has got a choice, they can either respect the wishes of Scottish people or face indyref2. They have to decide, either accede to Scotland's long-term and legitimate interests or face that referendum.

"If the UK Government ignores a Scottish parliament vote against Brexit it would indeed put us in a position where an independence referendum was likely."

Salmond said such a vote was also likely if the Tories continued with the approach taken by Chancellor Philip Hammond, who ruled out a separate Brexit plan for Scotland during a recent visit to Edinburgh.

He said: "It depends, if they act like Philip Hammond then they will get their just deserts, but if they do begin to listen, as Theresa May promised when she first became Prime Minister, we will see what happens.

"The First Minister's paper will give us our guidance and strategy," he added.

However, a UK Government spokesperson accused Salmond and the SNP of issuing "damaging threats to rip Scotland out of the UK".

The spokesperson said: “We are determined to get the best deal for Scotland and the whole of the UK as we exit the EU. The Prime Minister has been clear that devolved administrations don’t have a veto on leaving the EU and damaging threats to rip Scotland out of the UK are the last thing people and businesses in Scotland want or need.”

Meanwhile, Green MSP Ross Greer said a Holyrood vote against Brexit “would make an independence referendum, on our own terms, more likely”, as he wrote to the First Minister calling on her to reject Westminster's “indyref sabotage”.

Greer said: “In light of reports that the Westminster government is considering denying an independence referendum until we’ve been forced out of the EU against our will, I’ve written to Nicola Sturgeon to ask that the SNP joins Green MSPs in voting against the triggering of Article 50 if we are able to do so.

"Inevitably that would make an independence referendum, on our own terms, more likely."

A Scottish Government source, in response to the Greens, said: “We have made it clear that Scotland must have the opportunity to vote on independence before the UK leaves the EU, if it becomes clear that is the best or only way to protect our national interests – and any Tory plotting to block that would only succeed in boosting support for independence."