Tobacco manufacturers have developed 57 ways to make cigarettes safer but have chosen not to use the technology, according to a study.

The problem is that marketing some cigarettes as safer would be to acknowledge that normal cigarettes are unsafe, campaigners said.

This would lead to difficulties fighting legal cases against cancer sufferers who blame tobacco companies for their ill health.

But the industry has hit back, saying the study is mischievous and based on unproven allegations.

Patents to protect health shunned

Pressure group Action on Smoking and Health (ASH) and the Imperial Cancer Research Fund (ICRF) published the report on Wednesday.

It claims the tobacco industry has investigated and patented technologies that could lead to "the safer cigarette", but has chosen to ignore them.

It lists 57 devices that would reduce the dangers to health of smoking. Details of all the patents and when they were filed are posted on the Internet.

Dr Martin Jarvis of the ICRF's health behaviour unit helped launch the report.

He said: "The cigarette is like a dirty syringe for taking the drug nicotine. What we now know is that the tobacco companies could have made it less dirty.

"Current products cause premature death for half of all long-term smokers, so even a small improvement could save thousands of lives."

Clive Bates, director of ASH, blamed the companies' reluctance to use the technology on their fears over the legal implications in outstanding cases.

He said: "They could hardly bring out a new product advertised as 'low cancer' or 'heart-safe' as it would send out a very unappealing message to smokers and cause serious headaches for their lawyers.

Clive Bates: "Time for the industry to come clean"

"If they couldn't market the advantages of the new products, how could they recover the costs?"

The groups are calling on the European Union to demand tobacco companies measure, disclose and then reduce all hazardous parts of tobacco smoke.

They say this happens with most other consumer products.

Working within legal requirements

However, the Tobacco Manufacturer's Association, which represents UK companies, reacted angrily and attacked the document.

John Carlisle: Condemned study

"Frankly, it's a mischievous document based on unproven allegations," said John Carlisle, spokesman for the association.

He said UK companies fulfill all legal requirements.

"We have always co-operated with government fully in terms of the requirements they need - for example on levels of tar and nicotine.

"We comply with all international standards that are demanded of us, and as responsible UK manufacturers would rather talk to government direct rather than be bullied by activities from a non-smoking lobby."

He said the association already worked alongside the government to assess modifications to tobacco products.

"We're happy with that arrangement and so is the government," he said.

He added that filing a patent did not mean the device would work.

But Dr Bill O'Neill, a science advisor to the British Medical Association, disagreed.

He said: "The tobacco industry files patent applications because it wants to protect its intellectual property.

"If it really wanted to generate open debate, it would publish its scientific data in peer-reviewed journals."

The scale of unused patents to improve safety of cigarettes
What the patents claim to do	Number of patents*	Published
Reduce tar	11	1974 to 1998
Remove or reduce carbon monoxide (CO)	14	1972 to 1997
Remove or reduce hydrocarbons	8	1971 to 1988
Remove or reduce hydrogen cyanide (HCN)	11	1971 to 1988
Remove or reduce nitrosamines (a suspected carcinogen in humans)	6	1979 to 1998
Remove or reduce nitrogen-based substances	14	1980 to 1998
Remove potassium nitrate	2	1978 and 1986
Remove polonium (a radioactive compound)	2	1971 and 1980
Remove metals carbonyls	1	1972
Reduce aldehyde	1	1988
Remove or reduce other miscellaneous compounds	7	1976 to 1998
Source: ASH and ICRF
*Some patents claim to have more than one benefit