SINCE the UK vote to leave the European Union in 2016, speculation about the timing of a second Scottish independence referendum has been high. However, the process of holding one is a complicated political and legal matter, and it is not entirely in the hands of the Scottish Parliament to make a choice on when, or if, it happens. The Sunday Herald spoke to some seasoned pro-independence campaigners to find out more about the scenarios the SNP and wider movement are grappling with.

AAMER ANWAR, LAWYER AND PRO-INDEPENDENCE CAMPAIGNER

"I think we could be in the position that, if there was enough of a movement and a mandate there for the Scottish Parliament, the SNP could call an advisory referendum [which is not legally binding]. That would put immense pressure on the UK Government and I think that would be tactical if Westminster looked like it was going to kick it [a second independence referendum] into the long grass. It would put a huge amount of pressure on the UK establishment to abide by the wishes of the Scottish people, but it would also pull people into the independence movement, to fight for it. There are people who may have been borderline, but if they see the Tories and the Westminster establishment respond in an insulting, patronising manner, then I think it would build a stampede for an ‘independence now’ scenario. That would force the UK Government to the negotiating table."

TOM DEVINE, HISTORIAN AND ACADEMIC

"I can't believe she [Sturgeon] would be politically naive enough to do anything until there's a reasonable idea of what will happen in the negotiations. The Growth Commission is going to take a long time to filter down. It's a complex document and it's going to take some time to adjust. There will be flank attacks from the Unionists, but nothing is likely to happen in the short term. It depends on what happens on the street as there's a continued drip, drip process with a number of things. There's the continued alienation from the government at Westminster. That's why the pro-independence vote has held up. Then there's the question of what's going to happen with Brexit and also do the SNP have a convincing economic plan for an independent Scotland. If I was in Sturgeon's place, I'd think it's not a good idea to go till it's clear about the direction of the Brexit negotiations."

ROBIN McALPINE, DIRECTOR OF PRO-INDY THINK TANK COMMON WEAL

"Demand has to be met with supply, it’s as simple as that. There are only two options here. There is a Section 30 order [the legal instrument required to hold a referendum], which requires Theresa May’s agreement, or there is the Catalan option. The first problem is that the Section 30 route could result in a very lengthy spell in the Supreme Court. The second problem is that I’m beyond sceptical Nicola Sturgeon will call a Catalan-style referendum. This is not about when and where we want this. We haven’t resolved the first part of that never mind the second. Either we have to have a clear and unmistakeable democratic mandate, or we need to put ourselves in such a strong position that Westminster cannot say no. That means we’ve got to be in a sustained position of 55 per cent in favour of independence, or more, in the polls. The idea that Westminster is under any obligation to give us a Section 30 order when we’re at 45 per cent in the polls – I don’t see that, and I know for a point blank fact that they don’t. It’s got nothing whatsoever to do with when we would like this to be and everything to do with the labyrinth of politics. There’s no shortcut through this."

JONATHON SHAFI, CO-FOUNDER OF THE RADICAL INDEPENDENCE CAMPAIGN

"The recent surge of independence activity and debate has been driven forward by grassroots mobilisation. This has had a major impact and is now forcing the question of when another referendum should be held. In particular it has applied serious pressure on the SNP to use its referendum mandate. This is not entirely in Nicola Sturgeon’s gift, as is often thought, because any call for a referendum would likely be opposed by the Tory government. If recent events tell us anything, it is that there exists a well-rooted, self-organised movement for independence. I think this would come to the fore in such circumstances in a display of mass, democratic protest. This would be a key element in ramping up opposition to attempts at spiking a referendum, shaping the political atmosphere in a way that individual politicians can't. Such mobilisations would weaken the legitimacy of the Tories, heap pressure on Labour and take the process into the hands of a social movement rather than a political party."