- Survey from The Ramblers and Mamillan Cancer Support exercise could save lives
- Even a small amount could cut diabetes and heart disease
- But one in three people don't manage to walk even 30 minutes a week
Active: Thousands of people's lives could be saved by more walking
Walking for 20 minutes a day could save 37,000 people a year from dying prematurely of cancer, heart disease and stroke, according to a report.
But one in three people can barely manage to walk for 30 minutes a week including everyday trips to the shops, work or school.
Just under half of those surveyed walk for two hours or less a week far below Government guidelines of 150 minutes a week, or 21 minutes a day.
Only one in 20 people in England does enough moderate physical activity such as walking to get the health benefits, says the report from The Ramblers walking charity and Macmillan Cancer Support.
It reviews research into the life-threatening consequences of inactivity, ranging from early death to a greater risk of serious diseases.
The report Walking Works found if everyone in England did enough walking to meet recommended guidelines each year it could prevent 36,815 people dying prematurely, 294,730 cases of diabetes and save 12,061 people going to hospital for emergency treatment of coronary heart disease.
Research suggests being inactive can take three to five years off your life and increase the chances of developing cancer, heart disease or having a stroke by 25-50 per cent.
A lack of physical activity is to blame for 17 per cent of early deaths in the UK, says the report, costing the economy up to 10billion a year through sick days, care costs and early deaths.
Opinion polls reveal nine out of ten Britons think walking is a good form of exercise that can keep you healthy.
But a third of people are very inactive, saying they do less than 30 minutes of exercise a week and objective testing shows the figure is probably higher, with more than half failing to exercise.
Only 6 per cent of men and four per cent of women manage 150 minutes of physical activity a week in England.
Nearly everyone could step up their walking, says the report, with only 4 per cent of people not able to walk or needing help to do so.
Dr William Bird, founder of Walking for Health and Intelligent Health, which promotes exercise schemes, said lack of physical activity is a more significant source of ill-health and premature death than obesity.
He said: 'You can be fat and fit, but you can't be healthy if you're inactive and thin. Britain has one of the most inactive populations in the world.
'The USA eats more but as a nation they move around more, despite the car culture, because they understand how much it matters.'
He said the NHS should change its approach so every contact with patients, from GPs to consultants, stressed that exercise was vital to health. 'You don't have to do it all in one go just ten minutes extra walking a day could save your life,' he added.
Ciaran Devane, of Macmillan Cancer Support, said: ' For cancer patients, being active can help manage some of the debilitating consequences of treatment and can even help reduce the chance of some cancers returning.
'Inactivity is a nationwide epidemic that must be tackled now before it is too late.
'Healthcare professionals need to ensure that they prescribe physical activity, such as walking, as an intrinsic part of a healthy lifestyle.'
Dr Bird said walking improves health by boosting natural killer cells, curbing inflammation and preventing damage to the 'energy battery' in cells.