London Mayor Sadiq Khan has written to Volkswagen asking it to pay Transport for London £2.5 million in compensation for congestion charge revenue lost following the diesel emissions scandal.

There are about 80,000 Volkswagen cars registered in London believed to have been fitted with the device that cheats emissions testing – a scandal uncovered in September 2015 – that meant owners wrongly avoided paying the congestion levy.

In his letter Khan (pictured) said there was “no excuse for the utter lack of action” the car company has taken in London since the “dieselgate” scandal broke.

"VW vehicles qualified for the congestion charge greener vehicle discount on the basis that they emitted less than 100g of CO2 per km and met the Euro 5 standard owners of affected VW vehicles claimed a discount to which they were not entitled," he says.

"I want to see a proper commitment from them to fully compensate the thousands of Londoners who bought VW cars in good faith, but whose diesel engines are now contributing to London's killer air.

"I also urge them to reimburse TfL the £2.5 million lost in congestion charge revenue, which I will use to fund a new schools air quality programme that will reduce the exposure and raise the awareness of school children in London attending schools in the most polluted areas."

Volkswagen is reported to have responded: “"Volkswagen products perform well in independent real world emissions testing against new cars in general.

"It is therefore difficult to understand why our products might be singled out for pollution penalties."

Up to 9,400 deaths each year in London are estimated to be due to illnesses caused by long-term exposure to air pollution.

The mayor has also asked VW for a progress update on their commitment to re-programme the defeat devices in affected vehicles and the expected completion date.