SNP leadership insist Holyrood has the power to block Theresa May’s Brexit Bill

This measure is the means by which MSPs agree that Westminster can legislate on what are normally devolved matters.

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While the UK Supreme Court ruled during the Article 50 court case earlier this year that the LCM – also known as a Sewel motion after the minister who oversaw the main devolution act – was merely a political convention, if Mrs May were to ignore the process and press ahead regardless, such a move would spark a constitutional crisis between Edinburgh and London.

The PM’s admission on Wednesday, that it was a “possibility” that an LCM might be needed, raised the prospect that Holyrood could veto the UK Government’s flagship legislation on Brexit.

This would put back the Brexit process by weeks if not months and thus, potentially, jeopardise the UK Government’s timetable towards getting a deal with Brussels by March 2019.

Ian Blackford, the SNP leader at Westminster (pictured above), made clear: “We certainly know this morning it is the case the Government is going to have to come to Edinburgh in order to get through an LCM."

He emphasised how his party’s approach would be one of seeking “compromise” rather than confrontation with the Conservative Government.

“Let’s not talk about blocking, let’s talk about how we can compromise, which can satisfy the interests of all parts of the United Kingdom," he told BBC Radio Four’s Today programme.

The Highland MP said there had to be a new meeting of the Joint Ministerial Committee to bring together the governments in London, Edinburgh, Belfast and Cardiff to discuss the way forward.

"Of course, it is right - and many people have said this - that the Scottish Government should be represented at the talks in Brussels.

"For us, it is about maintaining our ability to trade through the European single market, to have the benefit of the customs union and, as a consequence of that, free movement of people," said Mr Blackford.

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But asked if Mrs May was not compliant with such demands, he suggested Nicola Sturgeon’s administration could threaten action.

“Whatever you do in a situation like that is you don’t show your hand because it’s about negotiating the best deal for the people of Scotland.”

Asked if Holyrood could, therefore, use a veto to block the repeal bill, Mr Blackford replied: "Of course, that is there. But I am not talking about that. I am talking about the spirit of compromise. I am hoping that we can get some sense and a recognition that our interests are perhaps in this case not wholly at one with the rest of the United Kingdom.”

In response, asked about the possibility of MSPs seeking to use a veto to block the Brexit legislation, Mrs May’s deputy spokeswoman said: “As the PM has set out all along our approach has been about achieving consensus and we expect the Scottish Government to act in the best interests of the Scottish people and support what we put forward yesterday.”

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Asked if she though the Scottish Parliament did have a veto, the spokeswoman replied: “The Scottish Government itself has said it does not have the power of veto over the process of leaving the EU…The PM has always said our approach to this is about achieving consensus.”

Because the main repeal bill together with Brexit-related bills on fishing and farming will cover devolved competences, it is expected that one or more LCMs will be needed.

At present, it is thought constitutional lawyers from both governments are locked in complex talks about whether or not an LCM is needed.

No 10 stressed how the two governments were discussing "complicated legal matters" but made clear that there was not yet a "definitive answer" to the question.