LONDON – Scotland on Wednesday marks a year to go until its independence referendum — but separatists face an uphill struggle to convince voters to back a momentous split from the United Kingdom.

Charismatic Scottish leader Alex Salmond has brought his Scottish National Party closer than ever to its dream of independence, but opinion polls suggest only a third of Scots currently intend to vote in favor of breaking away.

A “yes” vote will mean splitting away from England, Wales and Northern Ireland, severing a 300-year-old union — not a decision the 5.3 million Scots are taking lightly.

“We’re one year to the biggest decision we’ll ever take as a country,” said Michael Moore, secretary of state for Scotland. “This is an argument about the head and the heart.”

Scotland currently has a devolved government, giving First Minister Salmond’s administration in Edinburgh control over a range of policies including health and education. But other big policy areas, including defense, foreign policy and welfare, are still controlled by London.

Voters now have formidable questions to weigh up. Will an independent Scotland be richer? How much clout will the tiny new nation have on the international stage? And from border controls to setting up a new army, how will it work on a practical level?

Prime Minister David Cameron’s Conservative-led government is pushing hard for a “no” vote.

“We want to continue to make the case for Scotland as part of a successful United Kingdom — something that gives us greater economic opportunity and security and a much stronger place in the world,” said Moore.

The “no” camp claims independence will be fraught with risks and problems.

Oil is one of them — up to 24 billion barrels still lie off Britain in the North Sea, mostly in Scottish territory. London and Edinburgh have yet to discuss how they plan to divide the revenues, while experts say an independent Scotland could be over-dependent on the volatile energy market.

Rejoining the European Union and NATO could prove a headache, critics claim. And then there is the small matter of Britain’s nuclear deterrent carried by submarines based in western Scotland, which anti-nuclear Salmond wants to evict if he is victorious.

All in all, according to professor Michael Keating, chair in Scottish Politics at the University of Aberdeen, “there’s a great reluctance amongst voters to go all the way to independence, because it’s seen as very risky.”

But Salmond insists Scotland will face a “much more certain future” if it goes it alone.

“I think there’s very substantial risks in staying as we are,” he said during an interview last month.

He paints a vision of an independent Scotland that is not only rich because of its North Sea oil reserves, but more egalitarian and pro-European than Britain.

He also stresses the things that would stay the same, from keeping Queen Elizabeth II as the head of state to continuing to use the pound — although London has said it could potentially object to this.

Salmond is considered a canny political operator who has pulled off impressive feats for the SNP before, bringing them to power as a minority government in 2007 then winning a sweeping majority in 2011.

But while he claims he can do so again, most experts believe his chances are slim.

“Opinion polls have been showing about 30 percent for independence for the last 20 years and we’ve seen very little change, even though the campaign’s been engaged for the last six months,” Keating said. “So Alex Salmond would have difficulty getting that up to 50 percent.”

One in 10 voters who plan to vote against Scottish independence will change or reconsider their choice if the U.K. does not grant the region’s Parliament more powers, an ICM Research Ltd. survey for the newspaper Scotland on Sunday showed.

Among those who are decided on the issue, 60 percent oppose breaking away from the U.K. and 40 percent plan to vote in favor. That lead shrunk to 55 percent versus 45 percent when respondents were asked to assume that a vote against will also result in no extra powers for the parliament, according to the poll. The referendum on independence will be held Sept. 18, 2014.

A majority of voters in all age groups oppose independence, while 1 in 5 respondents say they have yet to decide, the newspaper said. It didn’t give a margin of error.

ICM Research interviewed 1,002 members of the Scottish public online between Sept. 10 and 13. The results were weighted to the profile of all adults.

U.K. Deputy Prime Minister Nick Clegg told Scotland on Sunday that leaders must “look at the alternative vision to independence” and that he agrees with his Scottish friends who “want Scottish nationhood and identity to be more fully expressed in our institutions.”

Clegg’s Liberal Democrat party opened its annual conference in Glasgow, Scotland, on Saturday, with Clegg calling for party unity less than a week after former Education Minister Sarah Teather said she was quitting as a Liberal Democrat lawmaker because the coalition government’s policies on welfare and immigration made her “catastrophically depressed.”

Analysts say the likeliest referendum outcome is a “no” vote followed by an SNP bid to devolve more powers from London — an option, believed to have the backing of most Scots, that is being dubbed “devo max.”

Control over Scotland’s own taxes and welfare policy will be top of the SNP’s wish list, Keating said.

Ironically, he added, devolution may have ultimately killed off the party’s bigger dream of independence as many Scots are satisfied with the status quo.

They enjoy several benefits unavailable south of the border, including free university tuition and medical prescriptions, while the settlement goes some way toward soothing a historic sense of oppression by the English.

Could a “no” vote, then, spell the death of the SNP? Experts think not, pointing to the example of Canada’s Quebec province — where the separatists continue to govern, despite having lost two independence referendums.

“They’ve proved that you can survive a referendum defeat if you are a nationalist party,” said Iain McLean, professor of politics at Oxford University. “I’m confident the SNP will survive.”