You don't get much more Scottish than Alistair Carmichael. There's the name for a start. Plus the stout, proud stance and the lilting accent of a family of farmers from the remote, scenic Isle of Islay, where golden eagles swoop and soar over the sheer North Atlantic cliffs. Yes, that Scottish.

And yet here he is, thumbs in his belt, his back to Horse Guards Parade just next door to Downing Street, explaining why Scotland should stay with the United Kingdom.

Carmichael is the UK's Secretary of State for Scotland. He is a Liberal Democrat who was first inspired to enter politics by the establishment of the Scottish Parliament, but whose job is now to oppose the Scottish nationalists and push the case for a united kingdom, adding his voice to what the nationalists have dubbed ''Project Fear''.

''My own family since time immemorial have tried to fatten sheep off heather in a few square miles of … one of the islands off the west coast of Scotland,'' he says. ''My wife is English, my children are half-English. I don't want their grandparents living in a foreign country. And my experience is written across the rest of Scotland.

''I believe in the UK. I am proud to be Scottish, my Scottish identity is very important to me. I am also very proud of having a very strong British identity, I don't see that as something that diminishes in any way the passion that I have as being a Scot.''

Thanks to devolution, Scots today have ''the best of both worlds'', he says: local control over health, education, criminal justice, transport, their own parliament, while also being part of a bigger player on the world stage, a bigger economy that shares opportunity and shares risk, and offers a degree of shelter and protection.

''I just don't see the problem that independence is supposed to solve. It is a 20th-century problem.''

He's not alone. At the annual awards for the British record industry, David Bowie pleaded ''Scotland stay with us'' in a message read out by Kate Moss (provoking vitriol online, where one Scottish nationalist suggested he ''f--- off back to Mars'').

There are still many months until the referendum. But in the past month the rhetoric has become a little more urgent, and a little more rancorous. Partly, Project Fear (aka the Better Together campaign) has come to realise that, despite polls that still appear to give it a comfortable lead, the ''undecideds'' seem to be swinging almost uniformly towards ''yes''. And so it has started firing more warning shots across the bows of nationalism.

Ross Greer is part of the reason why the momentum is with the Yes campaign. He is ''communities assistant'' for the campaign, part of a vigorous grassroots movement modelled on the structure that propelled US President Barack Obama to his 2012 win.

''No one has built a campaign of this scale in Scotland before,'' Greer proudly boasts. ''There are clear parallels with the Obama campaign and its emphasis on community action. You're not going to win just by winning over the mainstream media. All the research we've done shows that people are far more likely to trust friends or family, or people in their own community, than a journalist or politician.''

Seven times more likely, says the research. So ''Yes'' realised they had to get out there and turn voters into activists. They now have tens of thousands of volunteers, recruited through more than 4000 campaign events across Scotland since May 2012. They have street stalls every weekend. They knock on doors. They hold community meetings. The volunteers are told to hunt down the undecided and identify them to head office. Head office will send them a letter, inviting them to a community meeting where an ''ambassador'' will answer their questions and persuade them to vote yes - but more importantly, to start telling their friends and family why they changed their minds.

''It's very focused, it's very targeted,'' says Greer. ''It's all about identifying who voters are and making sure they're getting information that's relevant to them, that motivates them to vote yes … That seems to be working very well for us.''

By far the biggest question he and his ambassadors get, says Greer, is simply ''can we really afford it''. Recently people have also begun asking about whether Scotland can keep the pound, and whether it will stay in the EU.

Raising these doubts has been a recent tactical win for Better Together. In its white paper launched late last year, the Yes campaign optimistically argued Scotland could keep the pound, backed by the Bank of England.

But in February UK Chancellor George Osborne rejected the proposed currency union. It actually gave a short-term boost to the Yes campaign (''they don't like being told what to do by people they didn't elect, and Osborne is the epitome of what Scotland does not elect but gets anyway'', says Greer) - but it seems now to be hitting home.

''In order to have a currency union you have to cede sovereignty, which is the opposite of acquiring independence,'' says Carmichael. ''So one of the major planks of the prospectus for independence has been exposed as unworkable … and if they can't even say what the currency will be, you can't say the independence proposition has any significant credibility.''

The three major political parties appear willing to offer further devolution to Scotland as an alternative to independence, including much sought-after control over taxation, which will de-fang one of the nationalists' perennial complaints.

And European Commission president Jose Manuel Barroso recently said it would be ''extremely difficult'' for Scotland to remain in the EU if it left the UK.

Others, such as Jim Currie, a former European Commission director-general, have disagreed, saying Scots have rights as members of the EU that they should not lose. However, it appears likely that Scotland would at least lose some of the opt-outs from European legislation that currently benefit the UK. ''I cannot see how any member state is going to offer an independent Scotland membership of the EU on terms that they themselves have not been able to get,'' argues Carmichael.

If you're an old-fashioned ''follow-the-money'' cynic, then the Scotland independence debate comes down to this: there are literally meters on each oil platform off the Scottish coast, ticking over and reporting back to Treasury in London, which tots up the royalties. When Scotland goes independent, they will report to Edinburgh.

Greer says he has a simple argument for those who ask if Scotland can afford independence. At the moment, Scotland gives more to the UK than it gets back, he says. But the financial question is more complicated. For a start, it is a geographic likelihood but hardly a done deal that Scotland would inherit the lion's share of the North Sea oil, which is already slowing in production and will run dry in a couple of decades, anyway.

Also, businesses (and shareholders) hate uncertainty. They want to know how much tax they are paying and to whom, what currency they're paid in, whose regulations they must abide by.

The SNP has promised an independent Scotland would lower corporate tax by up to 3 per cent. Until recently most corporations stayed independent on independence. ''The truth is we don't know [what difference it will make],'' one director of a medium-size Scottish oil and gas industry company told me last year. ''There are too many unknowns. Officially, we don't think it will make a difference.''

But as reporting season approached this year, several companies broke ranks. Insurer Standard Life, which has been based in Scotland since 1825, said it had contingency plans to move south of the border ''to ensure continuity of our business' competitive position and to protect the interests of our stakeholders''.

The same week, the Royal Bank of Scotland said a vote for independence ''would be likely to significantly impact the group's credit ratings''.

The following week, three FTSE 100 companies - Shell, Lloyds and Barclays - also complained about the economic risks of independence.

Ruth and Allan Hunter live in Inverness, and at the moment they count as a vote each way. ''We are pretty much polar opposites on this,'' says Ruth. ''When I first moved to Scotland [from England] it was great to be able to vote SNP. It was like voting for a local group who understood your local issues.

''[But] most people don't even understand what this vote is really for.''

She works in the medical device industry, and has seen a reduction in clinical studies run in Scotland because it is unclear if it will remain in the EU. ''[The two sides] are just slinging facts and figures at us that seem to contradict each other. Bottom line? Why can't we just go down the route of further devolution? I'm scared that Scotland is going to bite off more than it can chew.''

Allan, a proud Scot, admits the Yes campaign's manifesto is partly ''just guesswork''. But like many who favour a Yes vote, he yearns for a government more in tune with Scotland's largely social democratic population. ''The country has been so badly run recently that it's hard to imagine an independent Scotland could be any worse off,'' he said.

''I'm looking forward to voting yes in September, and hopefully ensuring a better future for my children and a stronger and more prosperous Scotland without the drain of London holding it back.''