Don't laugh, but it's possible that the Tories won't win the next general election. Sounds silly, I know, given that the polls, the press, why, the very scent in the air, insists that David Cameron is – in the words of today's Guardian front page – the "PM in waiting". Wherever he travels now, Cameron leaves audiences concluding that he looks the part: he has the manner, the confidence, that glow of imminent power. Even Labour ministers have succumbed to this sense of inevitability. Refer in private conversation to the Tories as the "next government", and they don't even blink in protest.

But they might all be wrong. It's still possible that even if Labour doesn't win in 2010, the Tories could lose, denied an outright victory: those expenses-fiddling MPs might escape a hanging from the voters, but still parliament could be hung. I'm not saying it's likely, nor even probable. If you've got £10 to hand over to a bookmaker, find something else to bet on. But it is definitely possible.

Start with yesterday's Guardian poll. The headline figures showed Cameron outstripping Gordon Brown on every measure of alpha male leadership: tougher and more decisive. But underneath was the news that the gap between Labour and Conservative is shrinking. Some pollsters have it at 10 points, which they declare "the bare minimum for a functional majority". If that lead melts into single digits, as it could under the hot lights of an election, then the Tories will be in peril.

But that's just the beginning. Those at Brown's side promise that the coming contest will not be a national but a regional election, won in marginal seats that exist in roughly equal numbers in the south, north and Midlands. They've written off their chances in the southern marginals, but swear they're ahead in the key northern seats and competitive in the Midlands: aided, they say, by the fact that the Tories' appeal shrinks the further they get away from London.

Denis MacShane, the Rotherham MP, testifies that Cameron strikes even those of his constituents who now loathe Labour as irredeemably southern and metropolitan; their response to George Osborne is even more hostile. In a recent council byelection in Barnsley, the Conservatives came fifth behind Labour, the BNP, local independents and Ukip. Labour's high command contrasts this with the enthusiasm for Tony Blair – and poll numbers north of 50% – in 1997, and says the Tories are nowhere near where they need to be. Pollsters don't wholly disagree, noting the "softness" in Tory support, measured by those who say they might yet change their minds, and the scale of the mountain the Conservatives have to climb – needing to increase their number of MPs by the order of 70%.

Look to the women, the Labour optimists say next. Among female voters the Conservative poll lead is smaller. That's why the heart of today's Queen's speech will be a new promise on social care for the elderly, aimed specifically at the 45- to 65-year-old women who are, say Labour strategists, "in the crunch" on care, either worried for themselves or their parents. The contrast will be clear, they hope, with Osborne's austerity message, which may have won plaudits from the well-cushioned commentariat but, they insist, repels regular voters. In this view, all that Labour canvassers have to say on the doorstep is that the Tories will have you working harder for longer: not a great vote-winner.

What else do they have up their sleeves? Downing Street has been studying hard the come-from-behind Conservative victory of 1992, helped by the presence of one of the lead operatives of that offensive around the current cabinet table: Shaun Woodward. That year the Tories hit their opponents by warning of Labour's "tax bombshell". In 2010 Labour is mulling a return of the compliment, warning that the Tories will drop their own bombshell – on tax credits, many of which help people on middle incomes. Another 1992 echo: Labour hopes to remind those in work and with a mortgage that they are, despite the recession, better off, thanks in part to ultra-low interest rates.

They plan, too, to reprise one of Brown's favourite tunes, running 2010 as a "many, not the few" election. That the Tories have not dropped their proposed cut in inheritance tax – which will give a £200,000 tax break to the 3,000 wealthiest estates – while promising to repeal the ban on foxhunting only hands Labour a bigger target. "Government will now be of the rich, by the rich, for the rich," says MacShane.

There's another potential Tory weakness. When the National Front was on the march in the late 1970s, Margaret Thatcher moved swiftly, luring rightwing voters back to the Tory camp by talking their language, warning that immigrants threatened to "swamp" Britain. But that option is not open to the kinder, gentler David Cameron, not without fatally undermining his brand. So a boost for Ukip and the BNP could split the right vote and see at least a few seats slipping from the Tories' grasp.

And, despite those stellar numbers in the ICM poll, Cameron is not without vulnerabilities. I'm told that one political communications professional – sympathetic to the Tory leader – asks his corporate clients what kind of strategy they wish to pursue: a Blair or a Cameron? The former is for those who want to tackle a difficult subject, the latter is for those who want to change the subject.

The focus-group-meisters say the first story that voters tell when asked to talk about Cameron is still the one about him cycling to work – followed by a car carrying his bag. Or it's the Tory spinners briefing that Samantha Cameron was wearing a humble M&S off-the-peg dress – only for it to be revealed that the dress was in fact tailored especially for her on the orders of the store's chief executive. Labour can still try to brand Cameron as a fake.

Put it all together, close your eyes, cross your fingers and, say Labour's most optimistic hearts, it could all come right on the night. The problem, says the former deputy leadership candidate Jon Cruddas, is that "this perfect combination of forces all have to come into line in time for election day". In other words, even if some of the strategists' hopes are realised, it's a stretch to believe they all will be.

What's more, plenty of those arguments wobble under scrutiny. Take the 1992 precedent. As an issue, tax credits lack the punch of income tax. And, even if Gordon Brown does analogise quite well to John Major, is David Cameron really Neil Kinnock, widely derided as "unelectable"? No. Labour is clinging to the belief that the race will tighten in the heat of an election campaign. But that's far from certain. Isn't it just as possible that Brown might look tired and clumsy, thereby reinforcing the Tories' time-for-a-change message?

Even if they buy the optimistic scenario, plenty of Labour MPs are not quite sure what to do with it. For some it only makes them more frustrated, proof that the coming election really would be winnable if only they had one last element in place: a leader who had not, apparently, been written off by the electorate. Others take heart, believing that somehow they can stave off defeat without taking that fateful step. But they all know that it would take a miraculous dollop of luck for everything to go the way the Brown team say it might. And, right now, not many are feeling lucky.