The $1 trillion G20 package to save the world economy should help boost fragile consumer and business confidence and avoid contagion, but is no silver bullet to end the worst financial crisis since the Great Depression.

Expectations had been low for the London G20 summit after a series of leaked draft communiques offered little more than the usual rhetoric on doing whatever it takes to fight the recession, amid public bickering over what that could entail.

True, there was no pledge of extra cash directly to boost economies but the $1 trillion figure on new financing, mainly through the IMF, impressed markets and helped send stocks sharply higher.

It raises the Fund's kitty to help countries by $500 billion and adds another $250 billion to the IMF's Special Drawing Rights - in essence printing money to help countries in need.

The leaders also agreed a $250 billion package to boost world trade, which is set to shrink this year for the first time since 1982.

The extra money for the IMF is probably the most significant as it should lower the risk factor associated with emerging markets and thus reduce the chances of trouble there spreading back to the rich world - the so-called negative feedback loop.

Officials privately say the IMF probably doesn't need such a huge boost to its crisis-busting firepower but the idea is that such a huge number creates "shock and awe" for financial markets.

They will then have confidence that no country is about to go bust because even the IMF cannot bail it out. This is a problem that comes about once in 100 years, and it needs a solution that comes in 100 years, officials say. The trade guarantees should also help getting international commerce moving again by instilling confidence, at little cost to public purses. This was much higher than the $100 billion Mr Brown initially said he was hoping for.

While all this should at least stop the crisis getting any worse and turning into a depression, it may not be enough to stop most major economies shrinking rapidly this year, together with the attendant losses of millions of jobs.

The key problem of getting banks lending again remains and won't go away until financial institutions can find ways of clearing their balance sheets of risky investments made in the good times that are now next to worthless.

The communique says it all: "Our actions to restore growth cannot be effective until we restore domestic lending and international capital flows."

For now, the jury's out on how long this will take despite the huge bailouts and the schemes for governments to buy up the toxic assets. But the G20 meeting was never going to be able to solve everything.

In fact, the first leaders' summit in November, just as the world had just faced what seemed like a complete financial meltdown, was initiated to repair the whole system.

Back then at least, it was meant to come up with a whole new architecture for the modern financial world in terms of regulation and future crises. That was before the economy sank even further, giving Mr Brown and the United States grounds to thrust the focus onto the more immediate problem of getting economies growing again.