SALVO define themselves as a “liberation movement”. A vanguard force pushing forward the boundaries of the constitutional conversation to the point at which they believe the people of Scotland will undeniably allowed to express their view on independence.

They are viewed – by their own admission – as a bunch of “weirdos”, clutching “archaic” documents like the Claim of Right, which has acquired hallowed status in some parts of the Yes movement.

Retired TV producer Sara Salyers, who founded Salvo less than two years ago, summarises their argument as follows: Scotland is either a colony or it is in a voluntary union with England.

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“Take your pick, British state,” she says. “Because we’re going to take that right out to the international community and force you, really force to answer which one is it.”

For their part, Salvo believe Scotland is indeed a colony and that past assertions that Scotland is in a “voluntary union” with England are false.

But either option, if proven in court, necessarily allows Scotland the right to pick its constitutional future, they say. 

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It’s heady stuff. Parts of Salvo’s arguments draw on international law, others on ancient constitutional Scots legislation.

Their plan is to put enough pressure on the Scottish Government over time to convince it to establish relations with a “friendly” foreign country to press Scotland’s case on the international stage.

This would, they say, end up in the International Court of Justice (ICJ) – the top court of the United Nations.

From here, they would force the UK Government to argue either that Scotland is a partner in a voluntary union – which they claim by definition means it is free to leave that union – or it is a colony.

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Salvo - who claim to have 7000 members - believe both options would force the hand of the British state to grant another independence referendum.

But constitutional expert Aileen McHarg of Durham University is unconvinced. She told the Sunday National that is a false dichotomy.

“There are plenty of countries that don’t recognise the right to secede,” says the professor of public law. “It doesn’t follow that the constituent parts of that country are colonies. That’s just a logical error, it seems to me.

“You’re going to really struggle to establish that Scotland was a colony in any sense.”

In this case, Salvo will argue, hey presto, Scotland must have the right to have another say on its constitutional future.

Here’s where the Claim of Right comes in. An ancient document from 1689, it may seem obscure to the uninitiated. But its significance as a constitutional document is indisputable, famously being cited in the successful 2019 court battle to overturn Boris Johnson’s unlawful closure of Parliament before that year’s General Election.

Salvo – and a number of others – argue the Claim of Right establishes the sovereignty of the people of Scotland. They view this as being in conflict with the English principle of the sovereignty of Parliament over the Crown, or in modern terms, the His or Her Majesty’s Government.

If the people of Scotland are sovereign, how can they lawfully be denied a say in their constitutional future, ask Salvo.

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“It’s a condition of the Union that the Claim of Right is ratified, it continues in Scotland and that means that the people that the people are sovereign constitutionally in Scotland,” says Salyers.

Popular sovereignty, Salyers argues, was an important part of pre-Union Scotland’s political landscape.

That is so key to Salvo’s project that they took the process by which a parliamentary session ended in Scotland for their name. No session could end without the people – by which they would have been defined at the time – being offered “salvo”, or redress for their grievances.

“That is an absolute exercise in acknowledging the sovereignty of the people,” says Salyers.

By citing the Claim of Right in a court case against the UK Government, Scotland will be able to prove it is being unlawfully denied a second referendum on independence, Salvo believe.

Again, McHarg is not so sure. It would be a “big leap” to attempt to establish a link between the Claim of Right – which sought to address a contemporary constitutional problem in settling the balance of power between the Crown and Parliament – and the cause of independence, says the professor.

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In any case, she argues that it does not follow that Scottish popular sovereignty trumps English parliamentary sovereignty.

“It wasn’t about secession at all. It was about who got to be king and on what terms did they get to be king.

“You might be able to make those connections [between independence and the Claim of Right] in theory but what you’re not going to be able to do convincingly is make those connections on the level of legal doctrine.”

Mapping the issues dealt with in the Claim of Right onto the current political scene is also “completely anachronistic”, according to McHarg.

But ICJ judges may see it differently if a case ever makes it before them.

Salyers said the group is in the process of hiring a lawyer to advance their work in the hopes this will get the Scottish Government to take them seriously.

“They tend not to want to be publicly associated with a fringe, very indy group,” she admits.

But the group do take legal advice, she said. “We have had things checked. We’re not rushing off making wild claims.”

They will not say which country they believe Scotland can persuade to take up its cause on the global state – Salyers said this is because they are “up against the British state” and fear this will harm their chances.

In the meantime, Salvo believe their key task is to change how independence is thought of and talked about as a concept among Scots – something Salyers describes as changing “the ground” of the debate.

“Historically, Scots have defeated much bigger opponents when we chose our own ground,” she says.