Scientists have calculated that each cigarette cuts on average 11 minutes off the life of a male smoker.

The calculation, published in the British Medical Journal, is based on the difference in life expectancy between male smokers and non-smokers and an estimate of the total number of cigarettes a regular male smoker might consume in a lifetime.

The researchers, from the Univeristy of Bristol, took their figures on life expectancy from a major study of the impact of smoking carried out by leading cancer expert Professor Sir Richard Doll.

They calculated that smokers were likely to die 6.5 years earlier than non-smokers.

They also worked out thast if a man smokes the average number of cigarettes a year (5,772) from the average starting age of 17 until his death at 71 he will consume a total of 311,688 cigarettes.

Based on these figures, each cigarette cost 11 minutes of life.

Crude calculation

The researchers admit that their calculation is crude as it relies on averages, assumes the health effects of smoking are evenly spread throughout a smoker's lifetime and presupposes that the number of ciagrettes smoked throughout a lifetime is constant.

"However, it shows the high cost of smoking in a way that everyone can understand," they write.

"The first day of the year is traditionally a time when many smokers try to stop. The fact that each cigarette they smoke reduces their life by 11 minutes may spur them on."

Clive Bates, director of Action on Smoking and Health (ASH) said on average a 20-a-day smoker is losing one day of life for every week of smoking.

He said: "As if that's not bad enough, smokers are likely to die a more painful death and spend longer being ill while they are alive."