By Joe Pike

Infighting, relentless accusations of negativity, financial problems, botched marketing campaigns, crisis talks, tears, tantrums and a whole lot of swearing: the inside story of Better Together is not as you might expect. During the course of more than 50 off-the-record interviews with key figures at the heart of the No campaign, my jaw dropped repeatedly.

The unlikely alliance of three pro-UK parties working together was a unique, bizarre and fascinating moment in British political history. But behind the soundbites and set-piece speeches, there was a different and far more human set of stories to be told.

Stories of how Alistair Darling threatened to quit, how Better Together was at one point close to bankruptcy, and how Gordon Brown attempted to seize control of Labour’s No campaign. Until now, no one knew the tale of how £50,000 was wasted on a TV advert that was too shocking to be shown, and how another piece of marketing inspired by the TV series Breaking Bad was scrapped because of the show’s focus on crystal methamphetamine production.

Better Together’s central strategy was to tirelessly focus on undecided voters – the "million in the middle" – and persuade them to vote No. Early internal research made clear that positive messages about the UK would not be effective. This group of swithering Scots was much more likely to change their minds when messages based on the risks and uncertainties of independence were used.

The difficulty was that, by spending so much time highlighting the perceived negativities of independence, the whole campaigning operation would soon be criticised for failing to articulate a positive vision of Scotland’s future.

The term "Project Fear" is a case in point. It was coined not by Yes Scotland, but by Better Together’s director of communications, Rob Shorthouse. At first, it was an in-joke, a knowing nod to the negativity of many of Better Together’s key messages and to the relentless accusations of scaremongering from their opponents. But it was soon seized on by independence supporters as proof that the pro-UK camp was relying on solely negative tactics.

Yet, despite all its challenges, the No campaign ultimately kept a kingdom united. But it also left Scotland more divided than ever before. As soon as the Prime Minister returned through the black door of No. 10 on the morning of September 19, Better Together turned, as surely as Cinderella’s carriage, into a pumpkin. The pro-UK camp had no clear plan for what to do after victory had been secured.

This was indicative of a campaign that had a solid strategy that, to its credit, it stuck to through a barrage of criticism. But it was arguably flawed in its execution. “I’m a stout defender of the strategy,” one experienced figure told me, “but the campaign was shambolic.”

Few could have predicted what happened next: a dramatic aftermath that saw the SNP turn their referendum failure into a stunning General Election success, almost wiping out their rivals, and creating a dynamic new force at Westminster. The party’s tsunami surge of support was central to the UK’s most unpredictable election in a generation.

One year on from Scotland’s historic vote, with an in/out referendum on EU membership on the horizon and the prospect of a second independence referendum at the top of the news agenda, there are lessons to be learned for both sides.

I was stunned by the number of pro-UK politicians and advisers I spoke to who said: “There’s going to be a second referendum, and we’ll lose it.” This sense of defeatism and of the inevitability of independence is perhaps surprising so soon after a decisive victory for the No campaign.

If there is to be a next time, many of the leading Unionist politicians (Gordon Brown, Alistair Darling, Danny Alexander, Douglas Alexander, Jim Murphy) will play little or no part. All five have retired or lost their seats. In such circumstances, Holyrood politicians will probably play a far more prominent role.

Memories of the referendum will loom over Scottish politics for years to come. Don’t just remember the division, but the unprecedented democratic engagement too. And remember that, behind the scenes, there was another gripping tale to be told.

Joe Pike (@JoePike) is a political journalist and author of Project Fear: How an Unlikely Alliance Left a Kingdom United but a Country Divided, published tomorrow by Biteback, £12.99 (ebook £8.99).