The researchers noted that industrial and non-domestic boilers, which are larger than those in private homes, are the main contributors in central London, which is not a highly residential area.

The study pinpointed the source of pollution by analysing the ratio of NOx to CO2 which differs between traffic and boilers, using long-term air pollution flux measurements taken from the BT Tower.

About a third is used in the 25m domestic boilers that heat our homes. A similar amount goes for electricity generation with the rest used by business and industry.