Prevailing wisdom insists Gordon Brown is already more or less finished as Prime Minister. Washed up, almost before he has settled into the prize he always craved, by blunders such as the 10p tax-band fiasco and the election that never was. Demonstrably unfit for the job because deep character flaws decree he is no leader - and can't even decide what he wants to do with power when it's in his hands.

"All political news is now interpreted through the refractive lens of Mr Brown's failings. His few good ideas go unrecognised; unrelated mishaps congeal into a narrative of defeat," contended The Economist last weekend, as it justified the astonishing cover-picture treatment that Ian Bell highlighted on Wednesday. Anatole Kaletsky was once a Brown fan. The headline above his Times column yesterday? "We're hurtling towards Enron government."

I kid you not. Enron government. The Ken Lay of British politics is also compared, by a normally serious-minded commentator, with Robert Maxwell and Conrad Black. Piling into the fray, the Today programme's John Humphrys couldn't wait to ask Brown if he wouldn't mind stepping down now. After all, according to other reasoned media commentary, Mervyn King, the governor of the Bank of England, is now warning that recession looms (The Daily Telegraph) but there will be no more interest-rate cuts until 2010 (The Financial Times).

What's there to stay for? With the economy - the keystone of Brown's earlier reputation for political competence - heading off a cliff, he should just retire to Fife now, before the fallout from soaring petrol and food prices and collapsing house values finally buries him. This claque of obituarists may yet have their way. However, it is not difficult to construct a rather different take on what the next few years might bring - a scenario that poses major challenges for all aspiring political leaders, and one that may yet offer Brown an opportunity to rehabilitate his battered reputation, even sneak another Labour majority against mounting odds.

If Mervyn King's analysis of what the next few years hold for our material prosperity is broadly correct - and, short of the more apocalyptic takes on the Bank's inflation report mentioned above, I have no reason to doubt that it is - the run-up to 2010/11 will be materially different from the years before 1997. Back then, as Ken Clarke never fails to remind us, after the dark days of the early 1990s, things were already getting better under the Tories. The New Labour project could capitalise not just on growing public disenchantment with 18 long years of Tory dominance; the electoral risks in trusting that Labour really had changed its ways were mitigated by the improving economic climate already apparent to voters by 1995 and 1996. They could afford to take a chance.

This time, as Mervyn King warns, the road ahead looks distinctly "bumpy". So the New Tory project, under David Cameron, still has to convince voters it can navigate the obstacles ahead better than Labour. So far it has tended to do that by stressing continuity. Just as Labour, in 1997, adopted Ken Clarke's tough spending plans for the first two years, so the Cameronians rule out dramatic tax reforms and stress sharing the proceeds of growth between higher public spending and greater fiscal prudence than New Labour latterly managed to achieve. All that, however, is predicated on an economy that continues to grow and a price environment that remains relatively stable.

King's big bumps ahead mean neither is now guaranteed - and that presents as big a challenge for David Cameron and his Shadow Chancellor, George Osborne, as it does for Gordon Brown and Alistair Darling. The initial New Tory take on the credit crunch sounded more opportunist than convincing. And they have yet to tell us what they would do about spiralling energy and food inflation. Try as they might, they cannot blame it all on their opponents. Gordon Brown, as Chancellor, watched, like the rest of us, the crude oil price rise from $11 a barrel in 1999 to $125 now. But even his sternest critics don't try to pin that one on him.

So, unlike the transition from Callaghan to Thatcher in 1979, some of the biggest potholes confronting the economy over the next couple of years are not Brown-made or even home-made. The three largest - the credit crunch in financial markets, the soaring price of oil and rampant inflation in basic foodstuffs such as wheat, rice and milk and their derivatives - are all, in essence, global in nature. Left unresolved, they will confront whoever forms the next government at Westminster from 2010 and, in equivalent measure, whoever forms the next government at Holyrood from May 2011. The dominant economic forces at work today are no respectors of national boundaries.

Their shorter-term consequences in the UK - a slowing economy and a period of materially higher inflation - will, as King makes clear, squeeze take-home pay and slow consumer spending. They will cost jobs, too, with numbers registering for Jobseekers' Allowance across the UK now up for three months in a row. Nothing yet suggests a labour-market crisis or industrial upheaval on anything like the scale over which the Callaghan government presided in the 1970s, but the impact of dearer mortgages, dearer energy and dearer food on weekly bills is already a potent factor in the Brown government's unpopularity.

So why should such a bleak economic outlook present this Prime Minister with any kind of opportunity? For the simple reason that he has two years left to do something about it. And he can do things, like the £120 tax cut put into 22 million low- and middle-income pockets from September, as part of the fix to defuse the 10p rate debacle, while demanding his opponents spell out what they would do differently. Brown can, legitimately, point to the $155bn in tax rebates George Bush is putting into American pocketbooks. Or the £15bn stimulus Spain's newly re-elected government announced last month to maintain "economic vigour". Even the Germans have contemplated a £3bn tax cut.

Our Prime Minister and his Chancellor arrived at their £2.7bn tax refund by a very circuitous route. But they've done it. And if Gordon Brown can help orchestrate fresh international action against soaring oil and food prices and deliver on some of the rhetoric about ungumming global financial markets, he may yet give his government some fresh legs. An economic crisis whose origins lie elsewhere but whose remedies require global leadership looks like the best chance he has left to save his political reputation from those intent on trashing it.