From positive bounce to floundering, from failure and under-siege leader to global saviour, Gordon Brown's premiership has seen more phases than a lunar astronomer. Yet as 2009 approaches, David Cameron and the Conservatives are banking on the political adventures of the prime minister having more twists and turns to negotiate before the electorate are asked their view on the Brown rollercoaster.

The current phase being enjoyed by the prime minister is that of the reborn Keynesian, who, faced with a changing economic future, turned to the remedy of fiscal stimulation, paid for by hiked borrowing. He is happy to be seen as the bold and determined leader who ripped up his own dogmatic, prudent commandments in favour of a claimed "universal consensus" that there was only one way out of recession - and that was his way.

The result? Brown isn't the saviour leading Britain out of a dark recession, it's the recession that's led Brown's recovery. It's helped turn a 20-point poll deficit into a drive towards catch-up that makes a spring or early June election next year look a serious option.

There's only one flaw in this, and it's the assumption that an ever-deepening recession will continue to reward the Brown-Darling partnership.

Cameron has already laid down his New Year bet that sometime soon in 2009 the trust in the saviour will turn to blame as the downturn worsens. And the timing of this switch? This is the key don't-know of the coming 12 months that will determine if Cameron's gamble to attack the government's fiscal expansion and borrowing as "flawed", and abandon his commitment to maintaining Labour spending plans, is a success or a failure.

In Cameron's analysis, Britain's "Italian" level of borrowing is creating a tax "bombshell" for future generations. Britain is borrowing to the absolute limit already, and yet a further £20 billion pounds is being added. The borrowing binge is an error, a mistake, a danger, unacceptable.

Cameron hasn't relied on any grey or diplomatic vocabulary or played economic and semantic games with the change in his party's position. He wants the government to be seen as irresponsible and focused on the short-term; he wants his own party to be seen as focused on spending restraint, looking ahead and being tough on recovery and tough on the consequences of of recovery. And, in a return to the Thatcher era, he wants his party to be openly seen as once again being on the side of sound monetary policy.

Once the self-proclaimed "heir to Blair", Cameron has morphed into the Tories' risk-taking leader, and just as Brown dumped prudence, Cameron has thrown off any pretence that both parties share the same views on the role of the state, where it works best and what it's there for. Come the election, as he has said, "there will be a very clear choice."

If Cameron's gamble is to clearly differentiate what his party stands for, what it would do in the current harsh economic climate, and what a Tory future would look like as opposed to more of Gordon Brown, he needs two things to happen.

He first needs the government's stimulus strategy to fail; then he needs Alistair Darling to pretend that it isn't failing and that only with another tranche of borrowing, another instalment of debt, will recovery come.

At this point Cameron and the Tory frontbench can't be seen to be celebrating the failure they predicted. No-one likes an economic smart-ass, even if they're right, and especially not when there's real pain being felt out there in the streets.

Everything at the moment points to further rounds of government first aid: more for the banks, more law-driven arm-twisting to force them to open their coffers, more help to other industries or specialist sectors of the economy seen as crucial to the recovery process. In summary, more money, and that means more borrowing, more debt. Judged against an accelerating downturn, where things are getting worse, not better, and where, against no evidence to the contrary, trust in the Brown-Darling rescue plan is all that's left, then Cameron's prognosis will begin to sound better and far more grounded in the realities of a recession economy.

As he said "There's no money left; Labour have spent it; Labour have blown it."

When this becomes not a Tory speech but the accepted economic reality of UK 2009, then the Cameron gamble will begin to show dividends in the opinion polls.

Far from being the "do-nothing" party - and it's difficult for opposition to do anything because that's the job of the government - the Tories suddenly become the we-tell-it-like-it-is party, with Labour the failed fantasists who bet the family's silver on borrowing their way out of trouble in a binge that increasingly looks doomed.

Forecasts like the one last week from the Centre for Economics and Business Research, which predicts that the economy will shrink by 2.9% in 2009, more than at any time since the 1940s, do little for electorate confidence when put up against the chancellor's prediction that the UK will return to growth in the second half of 2009.

Darling's forecast of a "shorter and shallower" recession, because of the action he's taking, suddenly looks like a political suicide note if it's measured against continuing consumer spending decline, falling investment levels, rising unemployment and a month-on-month casualty list of high-profile businesses that are being sent to the morgue.

An early election, so the logic goes, removes the spectre of failure from Labour's forecast because the general election would be fought on the two parties' own assessment of how things were going to turn out, not on hard economic evidence. Cameron's gamble at differentiation may work better if Brown waits and has to deal with the consequences of explaining why his saviour's halo has slipped a bit, why the claimed stimulus didn't stimulate enough, and why a generation has been left to pick up the tab for the debt binge.

At the moment it may be too early to say whether it's Brown or Cameron who'll be going to the window first to cash in their winning ticket. The only certainty is that whoever loses won't be given the chance to recover their loss.

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