© Getty Images Sadiq Khan wants VW to cough up £2.5m

As if Volkswagen didn't have enough on its plate, now it's facing a £2.5m compensation demand from mayor of London, Sadiq Khan.

Khan has written to the car giant after Transport for London (TfL) found that of an estimated 80,000 of the 500,000 VW cars registered to addresses in the capital, were fitted with illegal defeat devices. So many have escaped the congestion charge for years.

The devices reduced vehicle emissions during certification tests and for models with smaller diesel engines, they were so effective that in tests, the emissions produced were well below the level where the congestion charge would come into play. The owners involved wouldn't have had to pay it as a result.

In September last year, Volkswagen accepted it had installed so-called "defeat devices" on its diesel vehicles to beat official emissions standards tests and make cars look less polluting than they were.

TfL has now calculated it lost around £2.5m in congestion charge revenue as a resulted of VW owners claiming a discount they potentially weren't entitled to.

Khan said:

There is no excuse for the utter lack of action VW has taken in London since the ‘dieselgate’ scandal came to light.

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.

He urged the company to "reimburse TfL the £2.5m lost in congestion charge revenue", which he will use to fund an air quality programme for schools. Khan said that will "reduce the exposure and raise the awareness of school children in London attending schools in the most polluted area".

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

But he's unimpressed with only offering a software-based fix compared to the compensation and buy-back settlement agreed with US regulatory authorities for American consumers - deeming it "woefully insufficient" in comparison.