AS a former public relations man, you'd think the Chief Secretary to the Treasury would pick a less ominous location for an interview.

Danny Alexander's riverside constituency office in Inverness is flanked on one side by an enormous funeral parlour, while on the other the local pub has been turned into a "Yes cafe" by his opponents in the independence referendum.

But inside, beneath a portrait of Gladstone, a "No Thanks" mug of tea firmly in hand, the most senior LibDem in the Coalition after Nick Clegg is all smiles and betrays no hint of the threats hovering around his party or the No campaign.

It is a quirk of politics that David Cameron is often dismissed as vapid for doing a seven-year stint in PR for a TV company, but Alexander's decade in the same game, for pro-European pressure groups and the Cairngorms National Park Authority, is usually overlooked.

Yet it is evident in his every sentence - that reaching after the upbeat and inoffensive.

It is a useful quality for a politician, but one that can make him look too colourless to replace Clegg as leader if the LibDems crash in 2015.

Before that reckoning, he's getty ready for an August No tour of the Highlands, an area he reckons is "very much against independence".

Given the day job, it's not surprising most of his arguments touch on the economy, which he sees as "a very weak flank" for Yes.

"Most people can see that the economic arguments are all in favour of keeping the UK together. The inability of the Nationalists to answer questions in a straightforward way about independence, whether it's about start-up costs or currency or the wider economic issues, is something undecided voters find very troubling.

"It just multiplies in people's minds that independence is an incredibly risky and uncertain and dangerous business."

It is brave of him to mention start-up costs.

When the Treasury claimed the bill could be £2.7 billion, the LSE's Prof Patrick Dunleavy claimed his work had been "badly misrepresented" by the Treasury to produce an exaggerated figure.

Does Alexander accept that, in the words of his own Permanent Secretary, Sir Nicholas Macpherson, the £2.7bn was "misbriefed"?

"Well, em, it was purely illustrative," he says. "It was clearly, em, eh, it's been taken and perhaps was briefed to mean much more than it actually did. It's for Nick Macpherson to account for what has happened there. He's said what he's said and I don't dissent from it."

Then that PR training kicks in again.

"But actually I think that episode flushed out something incredibly important in this debate, which is the Nationalists don't know how much it would cost every Scot to set up a new state, and secondly that the Nationalists don't question the rest of our calculations for how much Scotland benefits [by £1400 a head] from being part of the UK." Nice pivot.

He also neatly inverts the SNP claim that a Yes vote is vital to save the NHS in Scotland.

Given the NHS is wholly devolved, it is "total nonsense" and "a sign of desperation", he says.

"I would say, 'Vote No to save the NHS'. If we become independent there will be less money to spend on public services. To make sure we can protect the NHS, you've got to vote No."

Keen to push LibDem voices in Better Together, he's nevertheless generous about Labour's input, especially Alistair Darling's as chairman.

"I think we've made the argument incredibly well. Alistair has done an absolutely superb job. He is measured and thoughtful and persuasive. I'm a firmly paid-up member of the Alistair Darling fanclub."

So what about the Tory MPs bitching about him?

"I don't know who is bitching about who. People should shut up and get on with campaigning."

He's a numbers man: what does he make of Ian Taylor giving £500,000 to Better Together, while the oil-trading giant he runs, Vitol, reportedly pays just 10.5% tax on its global profits?

"I think he's entitled to donate to the campaign ... and I welcome his support," he says.

A LibDem reshuffle is expected after the referendum. How would it look if the party failed to promote a woman to the Cabinet?

He havers about the decision being Clegg's.

But doesn't he have his own view?

"I would love to see a female Liberal Democrat Cabinet minister," he says finally.

Because the rumour at Westminster is that East Dunbartonshire MP Jo Swinson, who Alexander calls "one of our biggest talents", will replace Alistair Carmichael as Scottish Secretary?

"I think Alistair's doing a fine job as Secretary of State for Scotland. He's played a great role in this campaign. Those are decisions for Nick Clegg, not me."

If there's a No vote, Alexander insists more powers will be devolved to Holyrood, despite SNP warnings Westminster will ignore Scotland.

He nods at the picture of Gladstone, who first advocated "home rule all round" in the 1880s.

"I want to see as radical a package of further devolution as possible," he says.

"The delivery of the Scottish Parliament was something my party worked very hard to achieve.

"The Calman Commission, I was only Secretary of State for Scotland for 17 days but I made sure it was in the first Queen's Speech [as the new Scotland Act].

"At every stage, Liberal Democrats have been one of the catalysts of more power for Scotland. "We've used our position in government to that effect, and we will be at the forefront of making sure more powers are delivered."