Walking or cycling for just 20 minutes a day could save the NHS £1.7 billion towards life-saving treatments, according to new research.
The Greater London Authority says the cost of healthcare could be slashed over the next 25 years if every Londoner exercised for less than half an hour a day.
Currently, only around a third of people living in the capital manage to increase their heart rate for the recommended 20 minutes.
City Hall chiefs believe getting the blood pumping could help to prevent conditions such as dementia, stroke, diabetes and even cancer, while reducing health service spending.
The findings were revealed as London Mayor Sadiq Khan outlined his plans to improve Londoners’ health.
The Mayor’s ‘Healthy Streets for London’ blueprint focuses on reducing reliance on cars and encouraging travel on foot or by bike.
Will Norman, City Hall’s first full-time walking and cycling commissioner, will deliver the strategy.
He said: “Working with Sadiq to make physical activity a bigger part of Londoners’ everyday lives could have a truly transformational impact on our city.
“It will not only substantially improve Londoners’ health but play a key role in tackling our air pollution crisis.”
He added: “Increasing physical activity must be a central part of everything we do – building stronger, healthy communities and improving quality of life for everyone.”
The Mayor said the health strategy would also help to reduce pollution, boost mental health and combat social isolation, while bringing economic benefits to high streets across the capital.
Mr Khan also wants to tackle traffic congestion and address concerns over road safety.
He said: “The future health and prosperity of our city depends on us all boosting the amount of physical activity we do.
“With children’s health being harmed by our poor quality air, our bold new approach will focus on making walking and cycling a genuine long-term alternative to car use across more of London.”
He added: “The personal health benefits could also be huge if we can make our streets more appealing, encouraging more people to be more physically active as part of their everyday journeys.”
According to Public Health England, there would be an 11 per cent drop in coronary heart disease and an 18 per cent decline in Londoners dying every year if all Londoners walked or cycled for 20 minutes a day.