For a time there is a chance that the yoga class in room 16 of Islesburgh Community Centre in Lerwick will have to move, though in the end the pro-Scottish independence group across the landing, in room 12, does not need the extra space

The Yes Scotland meeting in the Shetland Islands' capital is one of hundreds that have taken or will take place before the Scots decide whether they should break away from the United Kingdom in a referendum on September 18th next year.

For now the polls are steady, with two-thirds or so of those questioned saying they are likely to reject the independence call led by the country's Scottish National Party first minister, Alex Salmond – though, in truth, most Scots have yet to engage.

At the well-attended room 12 meeting a few of the currents that will be significant in the months to come are discernible, particularly the SNP's need to ensure that the Yes campaign is seen as more than just an SNP front. The top table includes Yes Scotland's chief executive, a former journalist named Blair Jenkins; Scotland's SNP minister for education, Mike Russell; Celia Fitzgerald of Labour for Independence; and Brian Nugent of Free Scotland, which opposes membership of the European Union.

During a question-and-answer session a member of the audience speaks admiringly of the Scandinavian high-tax and high-quality-public-services model, though Russell quickly intervenes. “I am in sympathy with that, but we will never get it off the ground unless we get independence. We need to focus on that,” he says, conscious that talk of higher taxes will frighten some voters.

Labour for Independence, meanwhile, wants Labour to revert to its pre-Blair identity, insisting that while it is “open to the possibilities of nationalisation or renationalisation of energy and transport” it does not promote nationalisation for the sake of it.

The Greens and the Scottish Socialist Party object to the SNP’s preference for lower corporation tax; in sharp contrast, some of the hundreds of businesses that have signed up to back independence favour capitalism, red in tooth and claw.

The SNP “wants to keep the Greens, the Socialists and others on board to make it look like it is more than the SNP, but it would probably help if they were more in control of it. I suspect that they will take more control and tighten it up as time goes by,” says one close observer.

The breadth of opinion in the Yes campaign causes its own difficulties, as the middle-ground voters who will have to be persuaded if the referendum is to be won are exactly that: the middle ground and conservative with a small C, if not supporters of the Conservative Party.

For months the SNP, which rules with a majority in the Scottish parliament, in Holyrood, has sought to neutralise points of concern for voters: sterling would continue to be used after independence, and Queen Elizabeth would remain head of state. Also, Scotland would remain in the EU and Nato, though the UK’s fleet of submarine-carried nuclear weapons, held at Faslane naval base, on the Clyde, would have to go.

On each of these issues Salmond and the SNP have been wounded, particularly after Salmond's insistence, late last year, that the Scots' position in the EU was unquestioned led to an "EU liar" headline in the Scottish Sun, which had once supported him.

Yes Scotland and the SNP bridle over the campaign run by the anti-independence group Better Together, whose leading figure is the former Labour chancellor of the exchequer Alistair Darling.

Last month even anti-independence campaigners accepted that some of their people had over-reached when they claimed that independence would mean big increases in mobile-telephone roaming charges.

Nevertheless, fury and frustration are evident from some on the Yes side, who find that they are forever answering a new Better Together charge rather than laying out a vision for a new Scotland.

But there are questions. Before the referendum battle began in earnest, for example, the SNP demanded that control of immigration be devolved to Scotland from London; since then it has backed “a proactive immigration policy – with a Scottish green card for skilled, committed new Scots”.

On Wednesday there was a new spat after the Liberal Democrat secretary of state for Scotland, Michael Moore, warned that immigration controls with the rest of the UK would have to be introduced if independence went ahead.

Theoretically, Moore is correct. An independent Scotland remaining in the EU as a sovereign state would face pressure from Brussels to sign up to the Schengen free-travel agreement.

In practice the SNP can, with equal legitimacy, argue that the political reality facing everyone would mean that the UK’s existing rules, plus the Common Travel Area agreement with the Republic of Ireland, would continue.

But that would mean Scotland could not have an independent immigration policy, either now or at any time in the future, because otherwise the posts “along the border” that Moore warned about would become necessary.

In the eyes of the SNP Moore’s warnings are but the latest from Project Fear, as they refer to Better Together (though the tag seems first to have been thought up by people inside Better Together).

In their bid to ridicule Moore, however, the SNP’s language offered a clear illustration of the party’s efforts to convince voters that the choice before them in September 2014 is not a chasm to be jumped but a logical next step in a journey.

"A Yes vote for independence means completing Scotland's home-rule journey, so that we have the political and economic powers in Scotland to take the decisions that are right for Scotland," says Annabelle Ewing, an SNP member of the Scottish parliament.

“Independence means having the powers we need in Scotland, and a new relationship of equality with our friends and neighbours south of the border, including sharing arrangements where that makes sense, such as currency and head of state. That is the best of both worlds.”

SNP-style independence
But the number of things that would remain the same, including the currency and the head of state, raises questions about what SNP-style independence means. Until 2011 the party favoured membership of the euro; it dropped that in the face of the currency's crisis.

Today it backs a sterling currency union, but how much freedom would Scotland have over its budget in a situation where the remaining parts of the UK, particularly England, produce more than 90 per cent of its economic wealth, asks Alistair Darling. "If you go into a currency union, England, Wales and Northern Ireland would decide on our budget, on our tax and on our spending. And that is not independence. As we see in Europe, it ends up with an increasing amount of political union, so what is the point?"

Equally, some older voters have been concerned by pension worries, after warnings by the Institute of Chartered Accountants of Scotland that some UK-wide schemes would face problems if they are split up.

Meanwhile, younger voters surprise. The SNP moved mountains to ensure that 16- and 17-year-olds could vote, yet most are seemingly not only unimpressed but actively opposed to the idea, expressing a caution beyond their years.

Denying that Better Together believes it has already won, Darling insists that battle has yet to be truly joined, even “though as a politician I can tell you that it is better to be leading in the polls than to be behind”.

Unlike most House of Commons elections, every vote will have to be fought over: “In the general election all the attention, frankly, goes into half a dozen marginal seats. On this, whether you are in Shetland or Dumfries or Glasgow, your vote is of equal value,” Darling says.

Both sides, to different degrees, nurse the memory of the 2011 Holyrood election, when the SNP made up an 11-point gap to secure an overall majority – “the result that could never happen” under the devolution deal put together by the late Donald Dewar, of Labour, in 1997.

For the SNP success next year means a US-style ground-war campaign, where thousands of “ambassadors” – hairdressers are a particular target for Yes Scotland – will be armed with the arguments needed to persuade their neighbours and friends.

For now, however, a majority of the public has not engaged with the debate, has already decided how to vote or – and this may account for quite a few – has been irritated by the often unpleasant tone that has dominated much of the argument.

Much of the unpleasantness is to be found on social media, where public figures and organisations have been vilified for their opinions or actions, notably the Scottish soupmaker Baxters, which became a target when a member of the company’s founding family donated money to the pro-union campaign.

The difficult for many people is that they are not yet sure what Scottish independence means, as a Yes result would be followed by two years of exit negotiations with London.

The full scope of Scottish independence thereafter would be determined by that election, according to Angus Robertson, an SNP member of the House of Commons. “That will be the starting point for parties. It isn’t a fixed line in the sand,” he says. “This is wider than the SNP; this is not our property. I would be delighted to win the referendum in 2014 and overjoyed to see the SNP re-elected in 2016 as the first sovereign government, but we live in a democracy, so people might decide that they want somebody else to do it.”

The future is always as yet unwritten, says Blair Jenkins. “Independence is all about opportunity and the democratic right to make our own decisions according to our own priorities and aspirations.” For many, such freedom offers uncertainty, not opportunity.

Essentially, voters are being faced with a straight choice between independence and remaining in the UK when, in fact, most want something in between: more self-government than they have today but with some powers shared.

Last year the Scottish Social Attitudes survey reported that 35 per cent supported full independence, 32 per cent wanted greater devolution – the so-called devo max option – and a quarter favoured the continuation of the status quo.

Before the Yes Scotland meeting in Lerwick, Alex Salmond and his ministers had stood before an audience in the Mareel, the town’s well-equipped cinema and auditorium, for one of the four meetings with voters that the Scottish cabinet holds each year.

“I am 58 years old,” he told them. “For two-thirds of my life Scotland has been ruled by governments which I didn’t vote for. Scotland has voted one way, but we have got a different government in Westminster, which is not democratic.”

It is an argument he has made at every opportunity, and he will continue to do so; it could become particularly powerful if the Conservatives’ summer rise in confidence is matched by improving opinion-poll figures.

Since devolution, in 1999, during which time it has been led first by Labour and then by SNP minority and majority administrations, Scotland has drifted away from the rest of the United Kingdom, believing that it follows a more social-democratic tune.

The belief has foundations. Tuition fees are not imposed on third-level students, the privatisation of parts of the National Health Service has been resisted; prescription charges have been abolished; and London-ordered welfare reforms are sharply more unpopular.

The crucial middle ground to be convinced are Labour supporters in the west of Scotland, who vote Labour tribally; they will be convinced only if they are sure that the continuation of such services, and their development after independence, will not bring higher taxes – or at least not for them.

If, a little more than a year out from the referendum, the Scottish National Party faces challenges, then so do those who want to continue the union with the rest of the UK, even if at the moment everything seems to be going their way.

The links with the Conservatives are difficult, and could, depending on the political landscape, become poisonous; while voters will demand to know what they are offering in terms of more devolution the closer polling day draws near.

Here there are problems, as the Conservatives, Labour and the Liberal Democrats have different thoughts, but Scottish voters were sold a pup in 1979 when they rejected a Labour offer of devolution on the promise of a better one from the Conservatives, which never materialised. If they reject independence they will not make the same mistake again.