Pollution wipes out the benefits of walking, a new study suggests. Researchers from Imperial College London found that the toxic air in built-up city centres prevents the positive effects on the lungs and heart which are usually gained from exercise.

Although the experiment was carried out in the over 60s, the scientists say the effects could apply to other groups, and have called for stricter air quality limits, and greater access to green spaces.

To determine the impact of pollution on exercise, researchers asked 119 people to take a two-hour stroll through London’s Hyde Park and also Oxford Street, a busy shopping area.

Levels of black carbon, nitrogen dioxide and fine particulate matter in Hyde Park are typically well within healthy boundaries but air in Oxford Street regularly breaches dangerous pollution levels, as defined by the World Health Organisation.

The researchers found that everyone in the study benefited from a stroll in the park, with their lung capacity improving within just one hour, an effect which lasted for 24 hours for many people.

By comparison, a walk along Oxford Street barely registered any improvement at all.