More than 95% of the world’s population breathe unsafe air on a daily basis.

That’s according to a new report from the Health Effects Institute (HEI), which said poorest communities are most negatively affected and suggested there is now an 11-fold gap between the most polluted and least polluted areas, compared with a six-fold gap in 1990.

In cities, much of this pollution comes from factories and transport, while in rural areas, air pollution is more commonly found indoors, caused by burning solid fuels.

The study says around a third of all people around the world have to deal with unsafe air both indoors and outside.

The HEI believes air pollution causes six million deaths each year, making it the fourth highest cause of death globally, following high blood pressure, diet and smoking.

However, the report added that things were improving, with many countries moving towards cleaner forms of cooking and transportation.

Bob O’Keefe, Vice-President of the Health Effects Institute, said: “There are reasons for optimism, though there is a long way to go. China seems to be now moving pretty aggressively, for instance in cutting coal and on stronger controls.

“India has really begun to step up on indoor air pollution, for instance through the provision of liquefied petroleum gas as a cooking fuel and through electrification.”