Iain Macwhirter on Labour crisis

Can Harry Potter save Gordon? Or is the PM's situation now so dire that not even the supernatural can save him? The donation of £1 million to Labour from the Potter author, JK Rowling, only emphasised the depths of Labour's own credit crunch: the party is £18m in debt. And with Labour 20 points behind in the polls last week, it was looking like the Deathly Hallows for Labour at their Manchester conference.

But the collapse of capitalism came to the PM's rescue. Labour MPs are daring to hope that the greatest economic crisis in 70 years may have been their leader's salvation. The tumbling banks eclipsed the rebellion in the ranks, led by the erstwhile "Blair babes" like Siobhain McDonagh who had been demanding nomination papers to precipitate a leadership contest. The astonishing resignation of the mild-mannered and intensely loyal Scotland Office minister, David Cairns, passed almost unnoticed midweek, as did a rebellion of grassroots Labour activists, who registered their lack of confidence in their leader in a poll for The Independent. There were just other things on everyone's minds.

The global financial crisis also gave Gordon Brown an opportunity to show he can command events as well as be overwhelmed by them. He personally intervened to ensure an orderly merger between HBOS and Lloyds TSB - an action which may have been unnecessary but didn't seem so at the time. Then he introduced a temporary ban on short selling in the City, and promised he was going to "clean up" the UK's financial system. This looked more like the Gordon Brown of summer 2007, when he seemed to be a competent and effective leader getting on with the job. Not flash, just Gordon.

But can it last? Well, there is no sign Brown's, or Labour's, unpopularity has been lessened by the events of the past seven days. The polls are dire. The Tories spiked to over 50% in a Mori opinion poll last week, for the first time since the height of Margaret Thatcher's popularity in 1988. Brown is, according to politics professor John Curtice, the most unpopular Labour PM in polling history.

And it is all his own work. Only a year ago, on the eve of the last conference season, Labour had a comfortable lead in the polls, and the talk was all about the troubles of the new Tory leader, David Cameron. Some commentators were forecasting a conference bloodbath for the Tories, over Europe, immigration and grammar schools - until Brown dithered over an early general election. From there it has been downhill all the way, with Labour's collapse mirroring the slide in the economy.

Generally, economic turmoil is bad for sitting governments, and with Britain entering what is likely to be a long and difficult recession, the omens are not good for a revival of Gordon's share price. Indeed, his apparent political recovery this weekend is looking a bit like the stock market boom on "Freaky Friday" - unsustainable and slightly mad. At any moment there could be another run on his political authority, organised by those nasty short sellers in the Tory Party who now smell blood.

Brown's fate is likely to be sealed by the Glenrothes by- election, once he calls it. Another catastrophic setback here will cause many in the party to dump their holdings in Gordon for good. Following the loss of Labour's third-safest seat in Scotland, Glasgow East, in July with a 22% swing to the SNP, and the safe seat of Crewe and Nantwich in May to the Tories on a 17% swing, the loss of Glenrothes, the seat neighbouring Brown's own, would be a huge blow. Left-wingers like Diane Abbott are joining an unspoken alliance with Blairites like Falkirk MP Eric Joyce to declare the by-election D-Day - or "Depose Day". David Cairns had also, apparently, been intending to keep his mouth shut until Glenrothes.

Labour MSPs were last week hoping the PM's decisiveness in merging HBOS with Lloyds TSB, saving thousands of Scots jobs, might have been enough to revive Labour hopes for Glenrothes. But there is now a nagging sense of betrayal about the merger, not least from some in the Edinburgh financial community who say it was mishandled. Standard Life chief executive Keith Skeoch has suggested HBOS could have been saved as an independent company if stock exchange rules had been observed and share dealing suspended early while merger talks were under way. This would have prevented the 50% share dive on Wednesday that sealed HBOS's fate.

Now Labour's Glenrothes by-election campaign is in crisis following the departure of Frank Roy MP, who had been due to act as campaign manager. It's not clear whether he walked out or was sacked, but this is looking like Glasgow East all over again, with the Labour campaign undermined before it has begun. The SNP are becoming immensely confident of victory and it is hard not to agree with them. It could be one of Labour's worst by- election defeats in history, and would plunge the government into crisis.

However, it's not entirely clear what is supposed to happen on Depose Day. Perhaps a series of resignations by junior government figures, coupled with appeals from various backbenchers for Gordon to "do the decent thing" and resign. No doubt appeals from ex-ministers like Alan Milburn, the former health secretary, who called for a change of direction last week, and Charles Clarke, who has already said Labour are heading for "disaster" under Brown. But it all seems to have got off to a false start. The bolt has been shot.

The PM's departure is not a foregone conclusion even after Glenrothes, though. For one thing, no-one in the Cabinet seems particularly eager to take on his job. One reason why Number 10 may have been so keen to get the names of the lowly dissidents into the public domain - Cairns, McDonagh et al believe they were "outed" by Brown's men - was to flush out a potential leadership challenger in the Cabinet. None emerged. David Miliband, the foreign secretary generally accepted to be the leadership-challenger-in-waiting, has been conspicuously loyal in his pre-conference interviews.

However, everyone in the Cabinet must surely realise that the game is up for Labour under Gordon, unless there is some magical transformation in the prime minister's personality. Perhaps they are all hoping Harry Potter will cry "salvio hexia" and awaken the "true Gordon" who will leap on his Nimbus 2000 to take on the Slytherin Tories at one final game of quidditch. It's about their only hope.