Tony Blair has said he will go to the gym more often

The Cambridge University study looked at over 25,000 people.

It found that stopping smoking, exercising more and eating better could give you the life expectancy of a person 11 to 12 years younger.

The government is backing the research, and launching an initiative to encourage people to make small changes to improve their health.

This is about showing people that there are everyday, simple choices they can make in their lives which will have a direct impact on their health

Caroline Flint, Health minister

The study, carried out in Norfolk, is part of the European Prospective Investigation and Nutrition (Epic) study, involving over half a million people in 10 European countries.

The UK arm of the study is following 25,663 men and women aged between 45 and 79 years old since 1993, looking at their diet, environment, lifestyle and health.

The participants have regularly filled in questionnaires about their diet, lifestyle and health and had periodic check-ups from nurses.

These latest results from the study showed eating five portions of fruit and vegetables a day can give you the life expectancy of someone three years younger.

Not smoking turned the clock back by four to five years.

Even increasing exercise by a moderate amount can take up to three years off.

But the amount of exercise someone would need to do to achieve that depends on their job.

An office worker would need to do one hour of exercise, such as swimming or jogging, every day, while a person with a moderately active job, such as a hairdresser, would need to take 30 minutes exercise a day.

People with active jobs, including nurses and bricklayers, do not need to do any extra exercise - as their work is strenuous enough.

'Daunting prospect'

Professor Kay-Tee Khaw, who led the study, said: "Many of us find it difficult to change our usual lifestyle.

"However, there is increasing evidence that even relatively small changes can make a big difference to our health and well being."

Government ministers highlighted the research as they launched an initiative called Small Change Big Difference, aimed at showing people how to improve their health by making small easily available changed to lifestyle.

Prime Minister Tony Blair has vowed to make lifestyle changes such as using the stairs instead of the lift, visiting the gym more often and boosting his intake of fruit and vegetables.

Public Health Minister Caroline Flint said: "We all know that we should eat more fruit and veg and get more exercise to improve our health, but sometimes improving our own health can be daunting.

"This is about showing people that there are everyday, simple choices they can make in their lives which will have a direct impact on their health.

"Eating an extra piece of fruit or walking up the stairs can help people add years to their lives."

James Johnson, chairman of the British Medical Association, said: "Today's campaign is to be welcomed.

"But we would also like to see funding questions urgently addressed if the agenda is to make a sustained difference to the health of our communities."