Independence isn't on the ballot at this week's Scottish Parliament election — but it's the issue at the forefront of voters' minds.

Elect a majority of pro-independence candidates on May 6, and they'll be saying yes to "indyref2" — a second referendum on leaving the United Kingdom. Deny the nationalists parliamentary control, however, and dreams of sovereignty slip away (for now).

Polling suggests the latter is unlikely, with Nicola Sturgeon's governing Scottish National Party (SNP) on course to win a plurality of seats. Should that come to pass, the party will waste no time in proclaiming a mandate for a fresh referendum.

"Scotland faces a choice of two futures. The long-term damage of Brexit and Tory cuts under the broken Westminster system, or the opportunity to secure our place in Europe and a strong, fair and green recovery as an independent country in a post-pandemic referendum," said Kirsten Oswald, the SNP's deputy leader in the UK Parliament.

Securing a second vote on secession is easier said than done, though. Before a legally watertight ballot can be sanctioned, the Scottish government must request a so-called Section 30 order from London, the legal apparatus that authorized Scotland's 2014 referendum.

This, in Sturgeon's mind, is the "gold standard" for securing indyref2 — but Boris Johnson isn't so keen. Though UK-wide public opinion looks to be shifting on the question of a second vote, the British prime minister has repeatedly rejected calls for a rerun referendum, arguing that a full generation must first elapse.

Could Sturgeon up the political pressure?

But Sturgeon believes this resistance will falter in the face of a pro-independence majority — and if not, she has a backup plan.

Sidestepping the need for a Section 30 order, the SNP would push its own referendum bill through the Scottish Parliament, inviting a legal challenge from Westminster. The UK's Supreme Court would then have to decide whether Scottish lawmakers have the legislative authority to approve a second independence vote. Experts believe it's a decision that could go either way.

"We really don't know which way the Supreme Court would rule on the question of the Scottish Parliament's competence to authorize a referendum. It's totally untested," said Kenneth Armstrong, professor of European law at the University of Cambridge.

"The British government might simply amend UK constitutional law, removing any ambiguity as to whether Edinburgh has the power to sanction an independence vote," he added.

Saddled with uncertainty, Sturgeon's indyref2 strategy has split the nationalist camp in two, with one branch favoring more strident action. Under the leadership of former First Minister Alex Salmond, the recently formed Alba Party — a pro-independence group competing with the SNP — is advocating a sharp increase in political pressure.

"Our tactics are many across widespread areas," said Kenny MacAskill, a former SNP justice secretary who defected to Alba. "There's international representations, there's legal action that can be taken and of course there's people's democracy as we begin to come out of lockdown: demonstrations and socially distanced gatherings."

Johnson isn't impervious to a ramping up of pressure — particularly if the polls show growing support for indyref2. Equally, he could decide to dig in, obstinately refusing a second referendum regardless of the political consequences. This would put the SNP in a very difficult position.

'We didn't vote for Brexit, we didn't vote for the Tories'

Assuming the legal route proves fruitless, Sturgeon would be forced to consider a so-called "wildcat" referendum: an unsanctioned ballot similar to the one staged by Catalonia's pro-independence government in 2017.

This is likely a non-starter for the Scottish leader, fearing a backlash from Brussels bureaucrats who could stymie dreams of rejoining the European Union post-secession. There are also doubts as to the viability of an unrecognized vote — opposition-controlled local authorities, who oversee Scotland's electoral process, could simply order a boycott.

This lack of clarity is, for some voters, emblematic of a wider uncertainty around the independence question.

"I don't trust the SNP anymore, I don't feel like they've got a clear plan for what independence would look like for Scotland," said James Glen, who voted for independence in 2014 but now backs staying in the UK. "I'm worried that if it goes wrong, fragile working class communities like my own will feel the most pain."

Support for separation remains strong, however, and there's palpable optimism in the ranks of those demanding indyref2.

"We didn't vote for Brexit, we didn't vote for the Tories. We need independence to ensure a commitment to social justice and to do away with the incompetence, cruelty and cronyism of Westminster," said Pat Byrne, an activist in Glasgow.

"I'm not sure when, but independence is coming."