Ideas that might have saved thousands of lives range from improved filters to cut the quantity of noxious chemicals reaching the lungs, to the addition of catalysts to change the chemical composition of the smoke. They have all been explored over the past 25 years.
The inventions have never reached the shops because selling a "safer" cigarette created the legal and marketing problem of admitting that existing cigarettes were unsafe, the Imperial Cancer Research Fund (ICRF) and Action on Smoking and Health (ASH) said in a joint report.
The claims were dismissed by the tobacco industry yesterday. A spokesmansaid the fact that an idea was patented didn't mean it would work in practice, or be acceptable to consumers.
Investigations by the charities have uncovered 57 patents lodged with the US patent office since the early Seventies and over 100 more submitted to its UK equivalent. They include designs for elaborate devices such as the "cigarettepipe with purifier" which incorporates a catalytic afterburner to ensure that incompletely burnt hydrocarbons are burnt more completely, reducing the tar levels.
The cigarettepipe would have needed a powerful suck to draw air through it, creating what is known in the trade as a "hernia effect", and would have left smokers with four inches of hot porcelain and metal to dispose of, making it impractical as well as expensive. However other, simpler, innovations such as the addition of catalysts to the tobacco itself, which work in the same way as catalytic converters in cars to absorb carbon monoxide and nitrous oxides, could have cut the incidence of disease caused by smoking, which claims 120,000 lives a year in the UK.
Confidential tobacco industry documents released during litigation in the US reveal the companies' reluctance to introduce these measures. An internal memo written in 1986 by Patrick Sheehy, the chief executive of British American Tobacco, said: "In attempting to develop a `safe' cigarette you are, by implication, in danger of being interpreted as accepting the current product is unsafe and this is not a position that I think we should take."
Dr Martin Jarvis, of the ICRF health behaviour unit, said smoke contained 4,000 chemicals, in addition to the nicotine that smokers want, which form the sticky residue in the lungs known as tar. "The cigarette is like a dirty syringe for taking nicotine," he said. "What we now know is that the tobacco companies could have made it less dirty. The current products cause premature death for half of all long-term smokers, so even a small improvement could save thousands of lives." He said the emphasis on "low- tar" cigarettes was misleading because evidence showed that smokers compensated by puffing harder and covering up air holes in the filters with their fingers.
Clive Bates, director of ASH, said the companies should be required by the European Union to disclose all the hazardous constituents of tobacco smoke and then reduce them.
However, medical specialists warned there was no such thing as a safe cigarette. Dr Angela Hilton, of the British Thoracic Society, said: "Although we welcome any steps to make cigarettes cleaner, the only way to reduce smoking-related illness and death is to increase the numbers of people stopping smoking for good."
John Carlisle, a spokesman for the Tobacco Manufacturers Association, said the industry had worked with governments over the past 20 years to make cigarettes safer and some innovations had been accepted while others had not. "Patents are lodged day in and day out but the fact that they are there doesn't mean that they work, are proven or will meet consumer desires. We will carry our research to produce cigarettes that are satisfactory for our customers and meet the requirements of government."
Liggett and Meyers, US, 1972: Chemical filter containing a mixed- metal carbonate; reduces hydrogen cyanide.
Philip Morris, US, 1981: New smoking material formed by heating carbohydrate and mixing it with a tobacco slurry; produces less tar and nicotine.
Fabrique De Tabac Reunies, Switzerland, 1986: Use of micro-organisms to improve tobacco; the micro-organisms consume nitrates and ammonium compounds in the tobacco, converting them to amino acids and proteins which are less harmful.
Japan Tobacco Inc, 1987: Cigarette incorporating fire retardant in its skin; reduces the delivery of tar.
No company, 1988: Filter made from the fruiting body of a fungus, Bacidiomycetes; absorbs tar, nicotine and other harmful particulates making the tobacco smoke taste light and mild. The filter is contained in a separate cigarette holder.
Rothmans, Benson and Hedges, Canada, 1996: Flavour reset technique; ensures that as the cigarette is smoked, flavour is maintained at a lower tar level, reducing tar delivered to the lungs.Reuse content