Julia Hartley-Brewer challenged a doctor over a statistic about premature deaths by air pollution following the action by doctors to try to remove diesel cars from the streets.
More than 300 doctors from the group Doctors Against Diesel signed the letter to Prime Minister Theresa May to warn of the risks in using the cars, which they claim can result in strokes, cancer, and dementia.
Norrice Liu, a paediatric doctor at Queen Mary University, had come onto talkRADIO to discuss this with our host.
Over the course of the interview, Julia questioned her about a statistic regarding 40,000 premature deaths as a result of air pollution and what that meant - in terms of how much time would be lost in minutes or hours.
She asked Norrice to clarify the position held by the Royal College of Physicians regarding this statistic, if it was to be used as a basis to change Government policy.