Joan Smith: Ed Miliband may soon be in No 10. Believe it

The instability of the governing coalition could fast-track Labour's new leader to Downing Street

Sixteen years ago last week, the Labour Party elected a new leader. It was a historic occasion, placing a youthful Tony Blair (he was 41) at the top of the party. Gordon Brown didn't stand in the contest and neither did Robin Cook, giving Blair an easy victory over John Prescott and Margaret Beckett. The election was deemed a huge success, setting him on course to be the country's next prime minister and supposedly putting an end to his power struggle with Gordon Brown.

In 2010, a very different kind of contest is taking place. The outcome isn't obvious and the front-runner, David Miliband, could lose to his younger brother, Ed, on second preferences. For two months, all five candidates have been slogging up and down the country, speaking at hustings where they make the same arguments and answer the same questions.

The hopefuls aren't always able to turn up in person and sometimes party members get their "representatives" instead, which is a bit like going to see Abba and getting to watch a tribute band. Meanwhile emails and letters pour in from the candidates, and their campaigners are phoning members individually to ask how they intend to vote.

None of this is exactly catching fire in the media where the repetitive nature of the exercise makes it hard to report. When The Times filled its front page with pictures of David and Ed Miliband looking strained at a hustings in North London on Wednesday evening, I couldn't help thinking that the headline – "Now it's personal: leadership battle tests brotherly love to destruction" – was straight out of "reality" television; in a contest notably lacking in fireworks, Cain versus Abel was always going to be an easy storyline. There is concern among Labour insiders that the contest has pitched two brothers against each other, but the anxiety isn't so much about the hustings as what might happen when the winner is announced in Manchester on 25 September.

Were Miliband D to lose to Miliband E, the former foreign secretary would have to make difficult decisions about his future. The Labour Party isn't so awash with talent and experience that it can afford to lose such a senior figure from the front bench. But having to serve under a younger sibling is hardly a comfortable outcome for an ambitious politician.

On Friday, David Miliband sensibly sought to shift the campaign from the personal to the political with an article in the Financial Times, where he accepted the necessity to cut the budget deficit but warned of the danger of "pulling stimulus" too early. It was Blairite to the core, repeating the message that business needn't be frightened of a Labour government, and inadvertently confirmed the elder Miliband's geekiness; if I were editing his campaign material, I'd put a red line through phrases like "maximising the multiplier effect of public services".

My problem with the contest is that the only real choice is between four Oxford-educated men. (Diane Abbott is too divisive to be a serious contender.) Harriet Harman is doing a good job as acting leader. She's the second woman to hold the post, following in the footsteps of Margaret Beckett in 1994, but Labour has yet to produce a woman candidate with sufficient status within the party to get the top job. It's almost as if Labour regards women as mother substitutes, who are allowed to comfort the party in times of crisis but who step seamlessly into the background once the "real" leader emerges.

At least the party is finally having an election. If you cast your mind back to 1994, which is the last time Labour held a leadership contest, John Major was prime minister, the Channel tunnel opened, the Rwandan genocide began, Sweden voted to join the EU, Saddam Hussein was still in power and Take That had two No 1 hits. The world has changed a great deal since, but Labour's managers thought they could get by perfectly well without asking members who they would like to lead the party.

In 2007, Brown was allowed to succeed Blair without facing a contest, despite the fact that he was manifestly unelectable. It's a worrying thing about political parties that they often can't see what's staring them in the face, and Labour's unwieldy constitution gives too much power to big beasts like Brown. It's difficult if not impossible to challenge a leader once he or she is in the job and Cabinet ministers risk losing everything if they call for change, a fact Brown understood all too well.

David Miliband didn't challenge Brown two summers ago when the then prime minister unleashed his attack dogs. Nor did he back the last-minute attempt by two former Cabinet ministers to force a leadership debate in January this year.

His supporters say that's all in the past. They also say that the former foreign secretary is the only candidate who looks a credible leader of the country, which may or may not be true – I'm inclined to vote for Ed Miliband first, then David – but it does raise the important question of what this contest is really about.

Some commentators have already written it off, assuming that the public is so well disposed to the Lib-Con coalition that Labour is stuck in opposition; according to this analysis, the party is choosing a caretaker and it doesn't really matter whether the outcome is Andy Burnham, Ed Balls or one of the Milibands.

They couldn't be more wrong: the instability of the coalition is daily more apparent, with Nick Clegg's gaffe about the Iraq war last week highlighting irreconcilable differences with his Tory partners. If I were David Cameron or George Osborne, I'd be having nightmares about the deputy prime minister's gasp-making inability to think on his feet.

Then there is the coalition's huge gamble on public sector cuts: if they bite too deeply, Lib Dem MPs will feel a great deal of heat from angry voters. If they work, the Tories may be tempted to break with Clegg and go for an early election, despite the promise to go on until 2015. Against this background, Labour might not have the luxury of five years to become electable again, even though the timing of the leadership contest is awful.

Political parties seldom make good decisions immediately after a defeat; the closest analogy is a woman leaving a hopeless relationship and suddenly having several plausible guys all trying to get dates. The Tories needed four attempts to get it right after 1997, but there are significant differences; Labour didn't lose that badly in May, and a great deal of the party's unpopularity was due to the unattractive personality of Gordon Brown.

There is always a tendency among political commentators to write Labour off, and on this occasion there's the added spice of a subtext about sibling rivalry. But when party members start completing ballot forms early in September, the exercise will be much more significant than an episode of Big Brother. If things go badly for the coalition government, the Labour Party might well be choosing Britain's next prime minister.