The UK’s “safe” pollution threshold should be cut by at least half, experts have said after new research showed just small levels can trigger heart disease.

The largest British analysis of its kind indicates that living near busy roads, even in otherwise quiet neighbourhoods, can expand the heart, making it harder to pump blood around the body.

The study found these “significant” changes took place following exposure at levels well below current air quality guidelines.

Scientists at Queen Mary University of London investigated links between alterations to the structure of the heart and exposure to pollution by examining the data of nearly 4,000 people over five years.

They focused on nitrogen dioxide levels and particles of pollution called PM2.5, significant because they can be small enough to enter the bloodstream via the lungs.

They found that for every microgram per cubic meter of PM2.5 and for every 10 micrograms of nitrogen dioxide the chambers of the heart enlarged by approximately 1 per cent.

However, the study found that the average annual PM2.5 exposure in the UK is between eight and 12, yet according to UK guidelines the safe threshold is 25.

More than 2.6 million people in Briton are living with some form of coronary heart disease, a condition that kills approximately 150,000 every year.