I am more confident of winning a Yes vote now than I was when I took on this job

In an interview to mark the final year of the referendum campaign, he told the Sunday Herald he was even more confident of a Yes vote now than when he took up his role in June 2012.

He insisted half of voters had yet to make up their minds, and claimed "the etiquette of Scottish public life" was behind a reluctance to come out publicly for independence.

Although one recent poll put Yes just a point behind No, most have shown support for independence in retreat, down to about 25%.

Elections expert Professor John Curtice last week said hints the Yes campaign was going backwards were "now clearly affirmed".

But demonstrating a relentless, almost frantic optimism, Jenkins said the reverse was true, with people increasingly backing a Yes vote.

"I think at some point the published opinion polls will catch up by the end of the year. I would expect to see some narrowing," he said.

"I feel more confident now of securing a Yes vote than I was a year ago.

"The experience of just talking to people around the country, of attending God knows how many meetings, and of having lots of data back from canvassing returns - everything I've heard and been told convinces me that there is a majority there to be won for independence."

He cites "anecdotal" evidence like friends he thought were pro-Union coming out for Yes to back up his claim.

"The etiquette of Scottish public life was that [independence] wasn't really a subject on which people would normally express an opinion.

"As we get closer to the referendum I think more and more people will find themselves forming a view.

"There is a natural majority for the key decisions about Scotland being taken in Scotland, and it's when people draw the line between that and the fact you only get that with the powers of an independent parliament that they tend to move towards Yes."

Another persuasive influence is the Common Weal idea of borrowing ­policies from Nordic countries to create a wealthier, less divided nation.

Common Weal shows "a different direction of travel is possible for Scotland as an independent country," he said. "There are elements of it, in terms of the social justice agenda and the fairer society, which instinctively I find appealing and I'm sure a lot of people in Scotland would as well."

By the time the year-to-go mark is reached, Jenkins will have been in post 448 days. He remains unbelievably positive about his campaign. "I come into work every day feeling it's a privilege to be doing this," he said. "This is a tremendous thing to be doing. It's the most fulfilling thing I've ever done."

But surely it's only human to have the odd doubt or dark moment? There's little sign of introspection. "I am much more Tigger than Eeyore in the way I approach life and this job. I am a very positive person. I always have been."

Although accused of being an SNP lackey, he disagrees with Alex Salmond's claim that the SNP's late surge in the 2011 Holyrood election is a precedent for a Yes win next year.

"I don't think you can say that a one-off referendum on Scottish independence is something that you can read across from a party political contest in Scottish terms."

Amid grumbling from Nationalist MSPs about the performance of Yes Scotland, Jenkins dismisses rumours of a rift with Salmond or the SNP.

"It's going according to plan," he said. "We've done what we set out to do, which is to build up the huge groupings of volunteers in every part of Scotland."

If Yes Scotland is failing to convert the public, you get the impression that Jenkins would be the last person to catch on. He has spent a year in meetings of like-minded souls, being "humbled" as he puts it, and having his own views reflected back at him.

But the Yes Scotland echo chamber is not the electorate in all its diversity.

And while his gravity-defying positivity will no doubt motivate staff and supporters, it may also be keeping Yes Scotland in blinkers.

Campaigns need cold-blooded stock-takes as well as Tiggerish cheerleaders.