Gordon Brown talks much about his Presbyterian past, but he has a story to tell - about personal morality, a sense of justice and a belief in the power of politics that does, at its best, appeal to the "better angels of our nature", as he put it on his first day in Downing Street. The nation needs someone who answers this description to lead it now, just as Labour needs to find someone who is able to set out a case for progressive government. Political reform can no longer be put aside as an abstract idea, of appeal to dreamers but not to voters who face the harder realities of life. The public is calling furiously for a better system. People want an honest parliament. They want leaders who are prepared to act. They loathe the old system, and many of the people who are part of it.

Tragedy

The tragedy for Mr Brown and his party is that his chance to change it has gone. Although he still purports to be a radical, he has adopted the caution of an establishment man. He cannot lead a revolution against his own way of doing government, and yet a revolution is necessary. Grandstanding on his claims to good intentions, the prime minister demands the right to carry on, even as the cabinet implodes around him. The home secretary, the chancellor, and perhaps even the foreign secretary may go, and Labour faces its worst defeat in its history on Thursday, but the prime minister does not recognise his direct responsibility for the mayhem.

The truth is that there is no vision from him, no plan, no argument for the future and no support. The public see it. His party sees it. The cabinet must see it too, although they are not yet bold enough to say so. The prime minister demands loyalty, but that has become too much to ask of a party, and a country, that was never given the chance to vote for him. Had there been a contest for the leadership in 2007 - and had Mr Brown called a general election - he would probably have won. He decided not to do these things. And he has largely failed since.

Any assessment must recognise the strength of Mr Brown's response to the financial implosion. When action to save the banks was needed, he acted impressively. But flaws in his character that drove his party close to revolt last summer now dominate again. He is not obviously able to lead. He blames others for failures and allows them insufficient credit for successes, as the current dismembering of Alistair Darling's reputation shows. He is only secure in the economic comfort zone he built up as chancellor, and in the company of his closest allies, such as Ed Balls, now being tipped as chancellor. The prime minister shines at the IMF or the G20, but the job involves much more than that.

Great causes win the day when people fight for them. A year of lingering emptiness beckons instead. Parliament is treading water; little is happening beyond the discredited attempt to sell off part of Royal Mail. Parts of government still function: on climate change, for instance, Britain is leading the way towards Copenhagen. But Mr Brown himself is not inspiring progress on these things. The McBride affair was poisonous to his reputation, but he did not seem to understand why. His timidity in the face of the expenses crisis has been painful.

The blunt reality is that, even if he set out a grand programme of reform now, his association with it would doom its prospects. Proportional representation would transform parliament, but if Mr Brown put a referendum on the ballot, it would be defeated because he backed it. A draft constitutional renewal bill was published more than 12 months ago - but what has come of it? This week Mr Brown announced a national democratic council that might (to see it in a generous light) form the basis of the sort of constitutional convention that led to Scotland's modern parliament. But it is too late. The chance for him has passed.

The next seven days will be crucial to Britain's political future. Jacqui Smith's pre-emptive resignation yesterday was the start of a reshuffle that Mr Brown may be imagining will defend himself from terrible election results. He is heading for the bunker. If Labour holds off now, at perhaps the last moment when a change of leader might be possible, it had better reconcile itself to sticking with its leader to the bitter end. The worst of all worlds would be for people to drag their feet, carry on supporting him when others desert, then desert too, late in the day, when it can only make things worse. During the next few days it will become apparent whether Mr Brown still commands sufficient support among his parliamentary colleagues to carry on. If he suspects not, he would win much respect by announcing that he will be standing down, and let his party choose someone who can use its remaining time in power to reform parliament and then fight the election with credibility.

The case for a new leader has been made stronger by the expenses crisis. Labour needs to enter the next election having reformed parliament. But Mr Brown will never do it. The prime minister was absent from the start of the debate and cautious now he has joined it. His instinct is usually to hesitate, and to establish reviews and commissions. Meanwhile, the chance of a generation is being missed. Only a Labour government, working with the Liberal Democrats, will bring about serious reform. The likelihood, for all David Cameron's promises, is that the Conservatives will not be radical enough, especially on fair votes. But Mr Brown has shown himself incapable of collaborating in this way. His disastrous announcement of expenses reform on YouTube showed that he cannot build the coalitions of interest (inside his party, never mind beyond) that are necessary for constitutional change. If reform is not to stall, someone else will have to lead it.

Rapid contest

The mechanics will not be easy to arrange. Change will always be a gamble. Mr Brown, on past form, may fight for his job. But he cannot last if his cabinet refuses to back him, faced with an inward-looking and isolationist reshuffle that leaves the prime minister at odds with the mood of his own parliamentary party.

Any handover should be rapid and democratic. There will have to be an election for leader, and clarity from the candidates about when they want to hold a general election. Labour's constitution is murky, and some argue that it would be impossible to hold a contest quickly. They worry that the party might squander much of the time it has left in power in debates and union votes.

They are wrong. The 2007 contest for deputy leader took less than two months. Former party officials confirm a contest now could be held in 23 days; the new prime minister could be in place by early July. Several ministers would make a better leader than Mr Brown, and want to stand. They should say so early next week.

After such a contest, parliament could sit longer into the summer and return early in September, as Nick Clegg suggested in the Guardian last week. A bill should allow a referendum on electoral reform on the date of the next election. There should be a guarantee that no former MPs and party officials will be sent to the House of Lords. A bill should be passed to establish fixed terms for parliaments, as works well in Scotland, setting the date for the next election.

The opposition will want one immediately, but a new leader can make the case for some time to establish themselves, for reform laws to pass and for parties to pick new candidates. They could also argue that David Cameron needs to be tested properly. An election now would see Britain stumble into the future without any idea where it will lead.

Before polling day, the public also needs to know the score on all MPs - not just that proportion subjected to the Daily Telegraph's treatment so far. The most open way to do this would be for every editor, and broadcaster, to be sent the disc now in the hands of one paper, with the onus of meeting data protection and defamation laws on the publishers. Parties will need time after that to find new candidates.

Progressive future

The needs of the Labour party and the country are obviously not the same. Labour members must ask themselves this weekend whether they think Mr Brown is best placed to put its values into action, and win popular support for them. The public, in tomorrow's elections, will consider whether Mr Brown is the right man to lead the country. And anyone advocating a change of leadership must make it clear whose interests will gain from it. This paper believes Britain has often been at its best when Labour has been at its strongest. People who disagree with that will welcome its implosion, knowing that it will make a Conservative landslide inevitable. That is why they are not clamouring for Mr Brown to go. Progressive thinkers do not have this luxury. Of course many people, who see the better angels in Mr Brown's nature, do not want his dreams to end like this. His premiership would be one of the briefest in history. He would never have fought an election. But fate can be unjust.

All must agree that the die is cast and a hard judgment made. Otherwise progressive politics will be dragged down at a general election in May 2010 that could lead to a much bigger defeat than Labour suffered in 1979. That might bring a chance for other parties to take it forward, as the Liberal Democrats are trying to do in this election. But they are not placed to enter government. Labour has a year left before an election; its current leader would waste it. It is time to cut him loose.