The weekly newsletter sent out on Friday by Fathom, a London-based economic consultancy, said it all. "It's getting really ugly out there," it said.

"It may be true that we have passed the first phase of this crisis, but that does not mean the next phase will not be worse, perhaps very much worse."

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The investors reading those dire warnings will already have spent their week seeing a heap of evidence piling up that the economic crisis is spreading around the world. Record after grim record was broken in the financial markets, as long-term interest rates sank to their lowest for decades, in some cases their lowest ever.

Any lingering hopes that some parts of the world economy, particularly the fast-growing emerging markets such as China, would remain immune to the crisis were snuffed out. With remarkable speed in the past two months, a
worrying but apparently manageable credit crunch has turned into a global financial crisis and a recession across much of the world's economy.

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• More than 80,000 jobs cut in just five days 

Perhaps the most alarming impact will be on the consumers of the rich world, whose confidence in the future will be vital in preventing recessions turning into depressions. Next week marks the traditional beginning of the US Christmas shopping season with "Black Friday", the day after Thanksgiving when stores see some of their heaviest business of the
year.

The term has traditionally been taken to mean the date that retailers' finances went into the black, or the heavy road traffic that used to ensue from millions of Americans making pilgrimages to worship at the retail shrine. But if the dire news from across the US economy has sunk in even among the world's most optimistic shoppers, it might instead mark another dark day for the US economy.

This week, perhaps the clearest possible signal of the trouble that US retailers are in came from their counterparts on the other side of the Atlantic.

Marks and Spencer, the store that above all others defines the British high street, announced a highly unusual snap one-day 20 per cent sale. Some described it as a "guerrilla raid", but in truth it was more like the return of fire in a skirmish with its retail rivals, which had already announced pre-Christmas sales.

But while one-off cuts in prices might tempt consumers to spend, economists warn that people might merely begin to expect that prices will continue to fall in the future, and so hold off spending.

The US economy in particular is likely to see headline inflation go negative next year, as the effect of the huge fall in oil prices takes hold and the American housing bust drives down the cost of renting and owning homes.

In theory, such deflation could be good for the economy, as it releases money for consumers to spend on other products.

But as Andrew Brigden of Fathom Consulting warns, deflation can also take a malign form. "The risk is that people don't spend because they think prices will be yet lower in the future and that sets off a negative spiral," he says.

Temporary drops in prices are unlikely to have that effect. But Mr Brigden thinks the combination of falls in commodity and house prices with weak demand means that US headline inflation is likely to go negative next spring and stay that way for months, dropping as low as minus 3 per cent.

"When deflation goes on for the best part of a year, expectations are more likely to become entrenched," he says.

Certainly any consumers watching the flow of news this week cannot have helped but wonder. Yields on two-year Treasury bonds, an indication of where investors think that the US Federal Reserve will set interest rates over the next 24 months, dropped below 1 per cent to their lowest level since the two-year bond was invented in 1976. British bond yields hit their lowest since the second world war.

The news from the real economy was bad. Over half a million American workers filed for jobless claims, 10 per cent more than economists' gloomy forecasts. Abandoning their usual studied optimism, Beijing officials described the Chinese employment outlook as "grim".

And the car industry continued to act as a powerful symbol of global industrial slowdown. The travails of the big three American carmakers have long been known, this week seeing another set of twists and turns on Capitol Hill as US lawmakers considered a federal bail-out.

But even their Japanese counterparts - long held up by Detroit's critics as the way American carmarkers should be run - showed they were being hit by the slowdown. Honda announced it would cut production this year by another
61,000 vehicles, adding the 5,000 employees at one of its British plants to the thousands of car workers around the world languishing at home on gardening leave.

At least oil is getting cheaper, though that is more to do with the threat of a precipitate drop in demand than a better long-term market balance.

The head of China's third-biggest oil company revealed this week that the mood among the state-owned oil giants was one of "panic" at falling prices.

And to cap it all, as if to set the seal on a week of threats to the world economy, there are pirates seizing huge ships in the Indian Ocean. These are strange and dark days indeed.