Banning lead in petrol is responsible for declining crime rates in Britain, the United States and other countries, startling new research suggests.

The astonishing conclusion threatens to overturn current thinking on crime and punishment. And it could undermine the reputations of leading politicians, including Rudy Giuliani, the frontrunning Republican presidential candidate, who is basing much of his appeal on the reduction of crime in New York City in the 1990s, when he served as mayor.

Published in the peer-reviewed journal, Environmental Research, the study reports a "very strong association" over more than 50 years between the exposure of young children to the toxic metal and crime rates 20 years later when they are young adults.

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And it says the association holds true for a wide variety of countries with differing social conditions, law and order policies.

Rates of violent and other crimes began falling sharply in the US in the early 1990s, and have continued to do so, followed by similar tends elsewhere.

Reducing crime has proved to be the foundation of the careers of many politicians who embraced tough law and order policies – none more so than Mr Giuliani, who not long ago boasted: "I reduced homicides by 67 per cent; I reduced overall crime by 57 per cent."

Yet evidence is growing that the banning of lead should take much more of the credit for reducing crime rates. The toxic metal has long been known to damage brains and to lead to criminal and aggressive behaviour.

Research at Pittsburgh University found that adolescents arrested for crime in the city had lead levels four times higher than their law-abiding contemporaries, and a study of 3,000 possible causes of criminality in 1,000 young people by Fordham University, New York, found that high lead levels were the best predictor of delinquent and violent behaviour.

The metal was first added to petrol in the 1920s to boost engine power and its use grew rapidly: levels in blood rose in parallel.It was phased out first in the US, starting in 1974, to be followed by other countries.

Britain – one of the last to get rid of the toxic metal – is one of the latest to enjoy a decline in crime.