Family doctors may soon be able to tell patients how altering their habits may help them to live longer - with the associated implications for private health insurance and the potential for reducing premiums.

Dr Chris Martin, a researcher and GP in Laindon, Essex, has developed a computer program that can outline how long a person may live, depending on simple information such as smoking habits, age and blood pressure.

By next year, Dr Martin hopes to have refined the model to include factors such as stress and ethnicity. People from the sub-continent, for example, are more likely to develop cardio-vascular diseases.

The results of his model are displayed in a simple graph that shows how many more years a person can expect to live after making changes to their lifestyle. The graph can show, for example, greater changes in life expectancy if a patient were to give up smoking, which affects the risk of lung cancer and heart disease. The program can also display the benefits of other lifestyle changes, such as lowering blood pressure and cholesterol.

GPs already use a risk calculator to evaulate how likely individuals are to have a heart attack but this is typically based on percentages, which Dr Martin says a lot of the public do not understand. His program, which he calls the Laingdon Model, produces a picture of the risks and the effects that different changes in lifestyle would have on lowering them.

Results are not displayed in percentages, but on a set of curves on a computer screen. These graphs show how likely a person is to still be living at any future age, up to 85 and how the chances can be improved by lowering cholesterol, quitting smoking or making other changes.

The graph shows that without making any changes, the chances of living to be 80 years old are around 25 per cent. But giving up smoking could increase that chance to fifty per cent.

A different graph shows that controlling blood pressure would also benefit life expectancy, but this does not make as great a difference as smoking. For example, a person who does not control their blood pressure has an estimated 80 per cent chance of living to be 60, but this can be raised to just over 90 per cent.

Dr Martin told The Telegraph: “I came up with the idea primarily to scare people out of smoking. And, anecdotally, it seems to work in at least half of the cases.”

He suggests three furthur changes that will help increase lifespan. The most beneficial is eating lots of fruit and veg, which will help to reduce the risk of heart failure and cancer. Doing plenty of exercise will also help to reduce the chances of developig heart disease. And reducing your stress levels can also help. But he told The Telegraph that there are no guarantees: “I deal in probabilities. Diseases in the body are biological car crashes. Some smokers will live to 85: most won’t.”

He tested the system by using information from a previous study, on a sample of people in Whickham, near Newcastle upon Tyne. Data was gathered between 1972 and 1974 about a group of individuals, who were chosen to representative of the general population. The group were then followed up for 20 years by the original authors of the study.

Dr Martin fed this information into his model, which estimated how many of them would have still been living after 20 years. His model predicted 75 per cent, whereas the follow up study showed that 75.4 per cent of the group survived.

He expects the models main use will be for GPs and for health advice. “If you show patients a graph it really brings it home to them,” he told The Times.

The model is already in use in some doctors surgeries in South Essex, after being taken up by Health Enterprise East, the NHS Innovations Hub for the East of England.

Dr Martin’s model was the subject of his dissertation when he was studying a course a Health Informatics at University College London. The MSc course is designed to help medical workers use their IT skills to improve patient care.