Last week was a bad one for bank shares; after the HBOS £8.5 billion loss, Lloyds shares fell by a third and other bank shares fell as well. Yet it was a very good week for the gold price, which closed on Friday at $935 an ounce, after reaching what was nearly a seven-month high of $953.30 on Wednesday.

Barclays Capital commented that gold prices were resuming their long-run bull trend after eight consecutive years of gains. For longer than the past eight years I have been arguing that investment in gold is an essential insurance against financial shocks. Last week was a classic example. Respectable British bank shares have now fallen by up to 90 per cent, while the gold price has risen by more than 200 per cent since Gordon Brown began selling the Bank of England's gold reserve.

I have been following the gold price since I published The Reigning Error, a short book on inflation, in 1974. I have not consistently advised people to buy gold - like all other assets, gold can become significantly overvalued, as it did in 1980. However, I have found that the movements of the gold price are one of the most useful pieces of evidence about the health of the world economy. Mr Brown's sale of gold was an avoidable error. My friend the MP Peter Tapsell repeatedly warned him in Parliament not to do it.

People buy gold when they are nervous about the economy, and they are right to do so because gold is a unique commodity. It has to a high degree two qualities that are seldom found together: liquidity and reality. It has strong liquidity; it can almost always be bought, sold or exchanged. There are other liquid assets, of which the US dollar is probably supreme, but they lack gold's quality of real value.

Dollars do not constitute a real asset, such as property or “real estate”. The dollar is simply a piece of paper. Gold has been a much better store of value than the dollar.

In 1873 one of the leading British economists, William Stanley Jevons, published a short book, Money and the Mechanism of Exchange. By 1887 it had reached its eighth edition. Unfortunately, there are few modern economists who do not suffer from the delusion that new truths make old ones obsolete.

Great mistakes could have been avoided in 2008 if bankers and politicians had studied Jevons, even though his little book was written 136 years ago. Jevons quotes Herbert Spencer as observing that “it is the grave misfortune of the moral and political sciences that they are continually discussed by those who have never laboured at the elementary grammar or the simple arithmetic of the subject”. That was true then, and it is true now. Indeed, there are still some people who believe that poverty can be abolished by the issue of printed bits of paper.

Nowadays such people usually call themselves Keynesians, though their doctrine is not to be found in the works of Maynard Keynes, a much less simplistic economist than some of his modern followers. These so-called neo-Keynesians are hostile to gold, usually for two reasons. They see gold as the natural enemy of the paper money in which they put their trust; they see gold-related systems as imposing a discipline on the unlimited issue of paper money, and they reject that.

World trade depends on the existing global system, which is one of paper currencies, separately managed and largely unconvertible. These currencies float in terms of each other, sometimes with a fixed rate in relation to a larger currency. Since President Nixon closed the gold window in 1971, there has been no fixed-rate convertibility between any of these paper currencies and gold. In the past 40 years the world exchange system has suffered from two periods of high inflation and is now suffering from the worst depression since the 1930s.

In 1873 Jevons could already write: “It is hardly requisite to tell again the well-worn tale of the over-issue of paper money which has almost always followed the removal of the legal necessity of convertibility. Hardly any civilised nation exists, which has not suffered from the scourge of paper money at one time or another... Time after time in the earlier history of New England and some of the other states now forming part of the American Union, paper money had been issued and had brought ruin.”

Daniel Webster's opinion should never be forgotten. Of paper money he says: “We have suffered more from this cause than from every other cause or calamity. It has killed more men, pervaded and corrupted the choicest interests of our country more, and done more injustice than even the arms and artifices of our enemy.”

In the 1930s some nations tried to beat the slump by competitive devaluations. In the present crisis, Britain has already experienced a very big devaluation of the pound, taking it down by a quarter against the dollar. Every country, led by the United States, has been issuing money, often in very large amounts, in order to bail out its banks. No one knows the total value of these national injections of cash into the banking systems. As the earlier injections have not restored stability to national economies, further injections inevitably will be made. All will be made in unconvertible currency, and overissue will occur.

Sooner or later the world's governments will have to reconsider Keynes's two real achievements, Britain's low inflation finance of the Second World War, and the world currency system that he negotiated at Bretton Woods.

Both Jevons and Keynes believed in the need for what Jevons called “a worldwide system of international money”. Without it, recurrent crises, such as the present one, will be inevitable. Governments need to create a new world system, in which gold, as a stabiliser, should play its part. For individuals, gold remains the best insurance against future shocks and the best store of value.

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