Air pollution is being blamed for soaring numbers of non-smokers who are developing lung cancer.
Doctors at leading cancer centres in London warned that high levels of pollution are causing a spike in cases of lung cancer.
They said, if the trend continues, the number of lung cancer deaths among non-smokers will overtake those who smoke within a decade.
According to The Times, there are more than 46,000 new cases of lung cancer every year in the UK.
And only one in 20 patients survives for more than ten years after the diagnosis.
About 90 per cent of cases are linked to smoking cigarettes but doctors at the Royal Brompton Hospital and Harefield NHS Trust have reported a spike in the number of operations they are performing on non-smokers.
This is despite the fact that smoking in the UK is at record lows.
Eric Lim, a consultant thoracic surgeon, said the number of patients treated at the centre between 2008 and 2014 remained constant at about 310 a year.
But, of those patients, the number of those who never smoked had risen from fewer than 50 to nearly 100 a year.
He said that the reasons for this change remained unclear but air pollution was a likely cause.
Cancer research groups have identified particles of soot in the air as being a carcinogen – something that causes cancer.
Some experts have argued that the study was too small to be reliable and suggested that the reason for the increase is improvements in machines that can detect smaller tumours.
Stephen Spiro, a former head of respiratory medicine at University College Hospital said: "There is no good evidence that lung cancer is becoming commoner in never-smokers.
"Lung cancer will become more frequent in never-smokers as a proportion, as smoking cancers begin to decline."