Mr Brown’s decision to suspend the indexation of petrol duties — originally intended as a temporary sop to the protesters, but then repeated annually and now indefinitely extended under threat of another anarchic revolt — was probably the biggest mistake of his political career.

The environmental arguments for higher fuel tax are so familiar they hardly need repeating. The fuel duty encourages people to do things that are good for the economy and society — travel less, use public transport, switch to diesel, drive smaller, more efficient cars. Moreover, and contrary to the propaganda of road-hauliers and farmers, fuel tax has no damaging competitive effects. A trucker’s competitive position cannot by definition be affected by a fuel tax that all his competitors must also pay. If foreign road hauliers fill up in Calais instead of Dover, British drivers can do the same. If British truckers are going out of business, it is because of excess capacity in their industry and cut-price competition from hard-working Eastern European drivers, not because of fuel prices.

As for farmers, whose incomes depend on government-administered prices and subsidies, it is hard to see why anyone should be moved by their complaints. Despite the “crippling” price of fuel for country people, Range Rovers are much more common in the country than they are in cities and few farmers drive Minis or Smart cars. Range Rovers are, of course, indispensable for driving across ploughed fields, but the case for raising fuel duties seems overwhelming as long as Range Rovers continue to race down motorways or crawl through the city centres on school runs.

But the best arguments for raising fuel duties are economic. The first is that oil supplies are managed by a global cartel, which has every incentive to keep driving prices up until they produce a serious fall in oil demand. If governments cut fuel taxes, this just gives Opec more leeway to push prices higher. If, on the other hand, Western governments increase their tax take, the prices received by Arab oil producers (and the fundamentalist charities that they finance) will be correspondingly reduced.

The second economic argument should be even more compelling to Mr Brown. When he capitulated to the 2000 protests, he lost a source of revenue that was almost as fundamental as income tax and VAT to the Treasury’s financial plans. The fuel-tax “escalator”, which did not just index petrol duties but automatically increased them above inflation each year, was arguably the most important single measure introduced by Norman Lamont in his courageous Budget of 1993, which put Britain’s fiscal house in order once and for all after Black Wednesday and paved the way for more than a decade of uninterrupted economic growth.

The escalator was carefully designed by Treasury officials to guarantee a steadily rising stream of revenue and to send an unmistakable signal that the cost of oil would rise inexorably year after year, making long-term investments in fuel economy worthwhile. By the time Mr Brown became Chancellor, the concept that energy was a desirable object of ever-rising taxation was so widely accepted that a doubling of the automatic escalation from 3 to 6 per cent annually in Labour’s first Budget hardly caused a stir. And from 1997 onwards, the escalator did its work as intended — encouraging energy conservation and simultaneously allowing the Labour Government to project a steady improvement in public finances without having to raise other taxes. Then, in that one mad week of road rage in 2000, Mr Brown threw it all away.

The true cost of handing over energy taxation to mob rule cannot be gauged by the £600 million that Mr Brown has sacrificed for the year ahead to buy off the possibility of this week’s disruption. The true losses can be measured from the revenues that would have been raised if the fuel-tax escalator had been left alone. According to calculations by the Institute for Fiscal Studies, the revenue forgone by Mr Brown because of his decision to abandon the escalator comes to a staggering £12 billion this year and steadily rising.

With an extra £12 billion in revenue from fuel tax Mr Brown could, for example, have repaid all the money he took from pension funds in his infamous £5 billion “pensions raid” and still have enough left to cut the standard rate of income tax from 22p to 20p. He could, alternatively, have used part of the money to remain within his public borrowing rules or to maintain the growth of health and education spending beyond 2007, when their present funding plans will run out.

In a sense, of course, this is all water under the bridge. There is no way that Mr Brown or any other Chancellor could now recoup the revenue he threw away in 2000, since that would mean raising fuel tax overnight by 60 per cent. Yet in reality, the benefits of a progressive policy of energy taxation are still there for the taking. The beauty of the fuel-tax escalator lay not in the specific sums it raised, but in the way it guaranteed a steady accumulation of revenue over a long period and simultaneously sent a clear message about ever-rising petrol prices. The steady rise in fuel prices ensured that consumers and businesses took the right decisions on energy conservation, while the guarantee of rising revenues introduced an element of reliability into public finances that Mr Brown has gradually been losing.

It is no coincidence that Mr Brown’s image as the fiscally prudent Iron Chancellor began to tarnish five years ago, at exactly the point when he capitulated to the fuel tax protesters. The price of this surrender, to the economy and to the Chancellor’s reputation, continues to rise every year.