It was while tucking into a breakfast of cereal and bananas in Downing Street yesterday that Gordon Brown finally decided he did not have the appetite for a general election.

The Prime Minister had slept on the decision, but by morning his instincts, honed from running three successful Labour campaigns, told him that he was not the only one who did not have the stomach for a snap November election.

The country had been whipped into a frenzy of speculation about an autumn poll, with the momentum seeming unstoppable only a week ago. MPs had been put on alert and had cancelled holidays, and the Tories and Liberal Democrats had raided their bank balances to pump cash into target seats. Last week, ministers had told their staff to take home files ahead of an announcement on Tuesday, after MPs returned from their summer break.

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But private poll evidence presented to the Prime Minister on Friday had shown that the public was struggling to understand why Gordon Brown wanted to go to the country so soon after becoming leader. With widespread approval for his time in office, and his handling of a series of crises, including an abortive terror attack, most people saw an election as a panic measure. "The public only want an election when they want to kick the buggers out," said one close ally of Gordon Brown.

To clinch matters, Labour's own research showed that that the Tories' tax-cutting promises at Blackpool had scored well not just in the national polls but among voters in crucial marginal seats. The Conservatives' policy of cutting stamp duty had gone down well with young voters, while women in Middle England's marginal seats in particular were impressed by the Shadow Chancellor George Osborne's plan to raise the inheritance tax threshold from £300,000 to £1m. "It became clear that the inheritance tax had had a big impact in the marginals," said one Downing Street source.

Around the breakfast table yesterday in the panelled No 10 dining room, the PM, flanked by his most trusted strategists, Ed Balls, Douglas Alexander, his election planner, and Ed Miliband, who had been in charge of drawing up Labour's manifesto, the mood for an election had changed from macho optimism to caution. Only 10 days before, buoyed by polls showing the party 11 points ahead of the Tories, Douglas Alexander had been gung-ho that Labour would easily triumph.

What had started two months back, primarily as a manoeuvre to wrongfoot the Conservatives and convince them to start spending their election millions, had gained a stunning momentum. Labour started believing its own propaganda that a snap autumn poll would not only consolidate the party's position and give Gordon Brown his own mandate for office, but would be the best chance of squashing the Tories, already in the electoral doldrums, for good.

But by yesterday, Mr Alexander, the international development secretary, had decided that although a victory at the polls was still likely, there were other serious complicating factors that agitated against calling an election, on Tuesday, as planned.

Not least was the fact that the electoral register was out of date and that thousands of people who had moved house or failed to register – many of whom were unemployed Labour voters – would be disenfranchised. There were echoes of the US presidential recount in Florida in 2000, when thousands of voters were left off the electoral roll and the Democrats lost the presidency by the most narrow of margins. "Douglas Alexander has been enthusiastic, but his position has switched quite emphatically to the anti position because of the voter registration issue," said a source close to Gordon Brown.

There were also concerns that the dark November evenings would not only shorten the campaigning day, but persuade many people to stay at home in front of the TV rather than face the trek to the polling booth. "This is not an urban myth," one Labour MP said. "Our vote does tend to come out later in the evening; it is often parents and elderly people who prefer not to go out after dark."

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The fact that the Prime Minister's crack election team had not been aware that the nights drew in early in November, nor that the electoral roll was out of date, was bound to be greeted with incredulity among MPs. There were signs yesterday that Mr Alexander may be being lined up as the fall guy for the decision to march the country to the top of the hill only to march it down again, after weeks of apparent indecision. Many have questioned why the PM did not put the lid on speculation earlier, before it bubbled over.

The Tories will not be slow to claim credit for Mr Brown's apparent volte-face. They were saying last night that he had effectively bottled it, a dangerous accusation for Mr Brown to face. He has struggled with the perception that he ducked out of challenging Tony Blair for the Labour leadership in 1994, and that he failed to strike to succeed him when political bravery might have brought about his succession much sooner. At Westminster, opposition MPs will seize on the apparent climbdown as a victory for David Cameron.

Attempts at rebutting the Tories' tax proposals during conference had backfired with accusations from Vince Cable, the Liberal Democrat Treasury spokesman, that Mr Brown had used Treasury civil servants inappropriately by getting them to cost the proposals. While the PM was adamant that the Conservative tax-cutting bubble could be punctured, he feared it might take time. If that can be achieved within six months, close allies of Mr Brown said yesterday, then the election would be back on. But, if necessary, the Prime Minister is prepared to wait 18 months to see off the Tories. The slowing economy may strengthen the case to go long and wait until 2009.

"We had to make a judgement call. If we can demolish their economic credibility they will have very little to say on public services for a long time. It is far better to exploit that in another six months to 18 months to two years than go now," said one Downing Street source.

Although the party was convinced it could win the election, it was highly plausible that Labour could emerge victorious from an election, but with a slimmer majority. Yesterday, Mr Brown decided it was not enough just to win an election. It had to improve on the majority of 66 Tony Blair won in 2005.

Friday, it now emerges, was crucial. Mr Brown and some of his closest aides were deeply affected by a presentation of "micro-polling" data from 150 marginal seats, given by his trusted pollsters Deborah Mattinson and Stan Greenberg, an American expert who has worked with President Bill Clinton. He announced he was bringing "good news and bad news" to Downing Street: effectively that he expected a Labour win, but that the volatility of the voters was such that he could not predict the margin of victory. For a leader defending a reputation, as well as a parliamentary majority that is effectively cut to 48 seats because of boundary changes by the next general election, such enduring uncertainty was key. Mr Brown promised to sleep on the cautious prognosis, which he had devoured along with advisers including Sue Nye, Spencer Livermore and Ed Miliband. Significantly, Ed Balls, one of the most powerful voices in favour of making the leap into the electoral unknown, was not present. Doubts over the wisdom of an early poll had begun to spread within the Brown camp earlier in the week. His tight, but growing, team felt the strategy was changing beneath their feet."They didn't announce it officially – they don't work like that," explained one Labour veteran called in to support the planning operation. "But it became known pretty quickly that something was going on. Gordon was having a rethink."

The rethink amounted to a hurried consideration of delaying the poll until 8 November – a week later than the date previously circled as the earliest practicable option. Mr Brown, it turned out, fretted that he might need another seven days for his great clunking fist to deliver a knock-out blow to the young pretender – and, particularly, the tax policies announced earlier in the week. Mr Brown's closest allies were divided.

While younger Brown acolytes, particularly Balls and Ed Miliband, are understood to have favoured the dramatic move, a number of "greybeards" in the Cabinet urged caution. Chief Whip Geoff Hoon spoke to backbench MPs earlier in the week, confirming his own opposition to an early poll. The Chancellor Alistair Darling and Secretary of State for Justice, Jack Straw, were in the more cautious bloc, along with the Secretary of State for Health, Alan Johnson. Nick Brown, a long-time confidant of the PM, is also believed to have favoured a delay. And the lights on the Downing Street switchboard lit up as Labour MPs in marginal seats questioned why he should gamble his premiership after barely 100 days, when he need not call an election for another two-and-a-half years.

But, as the media speculation grew and the preparations became more apparent, many MPs found themselves forced to "get with the programme" and reluctantly accept the reality of a looming election. With few aware of the growing consternation at the centre, the preparations in the field continued apace. Labour activists were parachuted into seats as regional parties tried frantically to fill holes in their candidates list. In Tory-held constituencies and target seats, campaigners, bolstered by cash from the millionaire Conservative backer Michael Ashcroft, were on high alert. "I have had teams on standby for three weeks. All our literature is ready to rock and roll," said one Tory MP yesterday.

But the climate of readiness did not last. Only hours later, those hired experts and specialist volunteers forming the nerve-centre of the looming campaign had more concrete evidence leading to a change in strategy. "We were told that we were stood down for the weekend, and that was taken as a clear sign that they had cooled," one said.

But it was only yesterday, when Mr Brown revealed in a BBC interview that there would be no early poll, that they knew they could relax after weeks of frenetic planning. So secret was the Prime Minister's decision at breakfast yesterday to shelve an election, that even those in his inner circle who only 48 hours before been in talks about strategy, were taken by surprise.

By the early afternoon, however, it was business as usual in Downing Street. As his young son attended a birthday party at Whipsnade Zoo with his mother, the Prime Minister was relaxing with a cup of coffee in front of the TV, watching England's surprise victory over Australia at the Rugby World Cup. It was a salutary warning that the favouritedoesn't always win.

Brown's 'campaign', by Derek Draper, Former Labour spin doctor

1. In Iraq with the troops

Like those before him, Brown wants to be seen as a serious, tough 'commander-in-chief'. In Britain our PM doesn't have that title, so the military photo-op is used to create the same impression.

2. In Iraq with flak jacket

He feels most comfortable in a suit and tie, though his tailor recently admitted that it was his mission to create a more casual look. Brown defaults to his 'politician's armour', even in the Baghdad heat.

3. At conference

Brown's advisers know the value of symbolism. He wears blue, and appeared at Labour's conference in front of a blue background. He's saying: 'You can forget the Tories. They don't matter any more. I am occupying their ground, as well as my own.'

4. With Bush

Here Brown's message is clear: 'Blair aped Bush, squeezing into jeans. I intend to be top dog, and Bush will be my poodle – sartorially, at least.'

Derek Draper is a former Labour adviser and psychotherapist with diy-therapy.com

Cameron's 'campaign', by Amanda Platell, Former tory spin doctor

1. At conference

Cameron is famous for saying he 'doesn't do clothes', and his advisers say his wife Samantha is always popping out to get him a tie either from Marks & Spencer or Next. Believe that, and you'll believe anything. I simply don't concede that Sam, a designer for Smythson of Bond Street, would buy hubby's ties in the high street.

2. Preparing a speech

With his conscientious high street look, Cameron is trying to distance himself from the alienating image of the Tory toff. The suits are always a bit ill-fitting, no hint of Savile Row. In style terms, he's definitely dumbing down for the mass middle-class electorate and trying to shake off his privileged public school image.

3. In shorts

Everything about this picture screams youth and voter appeal. It's also screamingly metrosexual – probably why that look disappeared so quickly.

4. The brown ensemble

This is Dave attempting country casual, and failing badly. He always manages to look a bit patronising.