Scientists and a leading anti-smoking group called yesterday for an overhaul of how toxins in cigarette smoke are measured after industry documents showed how they can be used to deceive smokers.

Tar and nicotine, the cancer-causing and addictive elements of cigarettes, are tested on machines. But because of the way people smoke, blocking filters or taking deeper drags on so-called light, the levels they receive are higher than that of a machine reading.

In a review of documents on smoking behaviour by Imperial Tobacco Ltd and British American Tobacco, researchers said BAT specifically developed cigarettes knowing this.

Professor David Hammond, of the University of Waterloo in Ontario, Canada, said the industry documents show BAT knew smokers compensated for the low tar by taking deeper puffs more often. So, although cigarette packs say the yields of tar and nicotine may be only a fraction of regular cigarettes, smokers receive much more.

A spokeswoman for BAT said the tobacco industry and health bodies acknowledge that ISO yields are not accurate measures for human smoking. Imperial Tobacco said it had not seen the report so could not comment on it.

The anti-smoking group ASH (Action on Smoking and Health) described the research published online by the Lancet medical journal as another example of the disgraceful behavior of the tobacco industry.

The charity Cancer Research UK said the report gives incontrovertible evidence that BAT has been completely aware that its light and mild cigarettes are as dangerous as any others. ASH says the measurements of tar and nicotine should be taken off cigarette packaging because they do not provide any meaningful information for consumers.

<B>Patricia Reaney</B>