Researches have described the "environmental injustice" facing commuters, who are exposed to up to eight times more pollution than car users.

Even though motorists produce the most pollution per commuter, they are the least exposed to harmful particulate matter (PM) as they are sealed off from the outside, a study by the University of Surrey found.

"We found that there is definitely an element of environmental injustice among those commuting in London, with those who create the most pollution having the least exposure to it," Dr Prashant Kumar, who led the study, said.

The team compared how commuters using cars, buses and the underground in different areas of London were exposed to a range of pollutants.