For 70 years we - like people all over the world - have been putting a known poison, especially toxic to children, into machines which spew it out in a fine aerosol, ideal for breathing in. Then we have moved the machines hundreds of millions of miles a day all over the country, ensuring that the poison is distributed as widely as possible. And, as a result, millions of small children over the years have suffered damage to their brains.
Now lead is finally to be banned from petrol on general sale - nearly 17 years after Mrs Thatcher's Government first promised to phase it out. Since October new Lead Replacement Petrol has begun to appear in the forecourts for those still using leaded fuel. And at the dawn of the new millennium, the long, frustrating battle to ban the toxic metal from petrol will finally be won.
Victory has been a long time coming. Oil companies have continued to make leaded petrol, long after its dangers have been accepted by doctors and governments, and substitutes became known. Millions of motorists have continued to use it, though their cars don't need it, and even though unleaded fuel has been available, cheaper, at the same pump.
Successive governments have dragged their feet: though Britain initiated the drive against leaded petrol in Europe, it has now fallen behind countries like Austria, Denmark, Finland, Sweden, Germany and the Netherlands which have already prohibited it - not to speak of the United States, which abolished it 30 years ago. Indeed, this week's ban has been forced on us in a European directive, courtesy of the European Parliament.
The amount of lead puffed into the air and the level of the metal in children's blood have been steadily declining as more and more cars have gone over, however slowly, to lead-free fuel. But, by the Government's own admission, one in 20 British children are now contaminated with lead above the level at which it is known to damage intelligence. An independent report by a senior scientist at Sussex University puts the figure at one in 10.
Lead has been known to be toxic for two millennia. In the first century AD the Elder Pliny warned of the dangers of freezing lead fumes, and some historians ascribe the decline of the Roman Empire to the high levels of lead found in Roman skeletons - the result of using it to line their wine vats.
And yet as industrial civilisation has advanced, lead has prospered. Detailed research shows that we contain about 500 times as much of the toxic metal in our bodies as did our primitive ancestors. Its use in petrol dates from 1921 when an American scientist, Thomas Midgley, invented a form of the metal, tetraethyl lead, that prevented car engines "knocking". (He later invented the first of the CFCs which attack the world's vital ozone layer.) At its peak, 7,000 tons of the metal were emitted from car exhausts in Britain alone each year.
Derek Bryce-Smith, now Emeritus Professor of Organic Chemistry at Reading University, was the first to sound the alarm. He became interested when, as a young post-doctoral fellow at King's College, London University in 1954, he asked the manufacturers for a sample of tetraethyl lead for an experiment.
"I got a phone call to say that they did not make it available because it was extremely toxic," he said. "They finally gave me some, but told me that if I spilt any on the floor I would have to take the whole floor up, and if I got any on my finger it would be absorbed through my skin and drive me mad or kill me."
He added that the manufacturers told him that they did not want to call too much attention to the poison because otherwise people might ask why it was being put into petrol. He adds that the firm was particularly worried because King's College was close to Fleet Street.
In the late Sixties he began to campaign against the use of lead in petrol. He became an early example of the whistle-blowing scientist, attacked by the scientific establishment and marginalised by his colleagues, who has eventually been vindicated.
"It was a very lonely battle for a very long time," he says. "A lot of my colleagues looked at me sideways, because many research chemists are in debt to the oil industry, which provides them with money for research."
Gradually his cause was taken up by a group of campaigners - led by a Wimbledon housewife, Jill Runnette, who put the issue on the political agenda. With virtually no resources they persuaded ministers to cut the amount of the toxic metal allowed in petrol by two-thirds - even though a Department of Health inquiry had concluded that lead in petrol posed little problem.
A painstaking American study of 2,000 children showed conclusively that lead damaged youngsters' brains. But the British scientific establishment and environment ministers still shied away from banning it all together. Once, an environment minister insisted to me that the metal must first be shown to damage British children too, as if they were a different species.
Yet the Government's own Chief Medical Officer, Sir Henry Yellowlees, warned in a secret internal memorandum that hundreds of thousands of British children were at risk. The crucial breakthrough came when Godfrey Bradman, the property developer, decided to help finance a drive to get the metal out of petrol altogether. He recruited the seasoned campaigner, Des Wilson, who ran a barnstorming assault - the Campaign for Lead Free Air (Clear) - which persuaded the Government, in little more than a year, to promise to phase it out.
Since then progress has indeed been leaden. During the Clear campaign over 90 per cent of respondents told an opinion poll that they would be prepared to pay more for lead-free fuel. In fact they were extremely reluctant to put it in their tanks.
When it was introduced, virtually nobody bought it even though it was no more expensive than leaded petrol; even after the then Chancellor, Nigel Lawson, adjusted fuel taxes so that it cost about 5p a gallon less than leaded fuel, only one in every 100 motorists used it. By the early 1990s the price difference had widened even further, but still half the cars that could use unleaded fuel were not being given it.
This adjusting of taxes in Britain has been sighted world-wide as a prime example of how using economic incentives, like reduced prices, can persuade people to buy cleaner products. In fact it tends to prove the opposite. Millions of people still went on buying leaded fuel, when their cars did not need it - paying much more for the privilege - when the only action they would have to take would be to put a different nozzle in the car. Even today, the Government admits, 2.3 million cars, which could use lead- free fuel, are running on leaded instead.
It is two European directives that have finally got lead out of petrol. The first laid down that from 1992 all new cars would have to have catalytic converters, to combat other pollution from car exhausts. These are poisoned by lead so the cars were made so that the nozzle from leaded fuel pipes could not physically be put into the tank. The other EC directive is the one that comes into effect this week.
Yet, even now, the Government appears to be preparing to exploit a loophole in the directive which allows up to 0.15 per cent of the nation's fuel to be leaded. This is to provide fuel for classic cars that can run on nothing else, but the Petroleum Industry Association estimates that only 10,000 tons of the over 120,000 tons available will be used in this way: the rest may be sold to ordinary motorists.
The Association admits that Britain could have gone lead-free years ago but says that this would not have been "cost-effective". Campaigners retort that this is putting industry's profits ahead of children's brains.
Meanwhile, Octel Corp, the British manufacturer which makes four-fifths of the world's lead for petrol, is now exporting almost all of it to the Third World, where an even greater crisis is brewing. New research in India has shown that more than half of the children in its major cities are contaminated with levels of lead known to damage intelligence - and with malnutrition having a similar effect the effects may well be devastating. The mass poisoning may end in Britain this week, but it continues over much of the most vulnerable parts of the world, and the battle to end it will run into the next millennium.