The Mayor of London has said that Volkswagen should pay £2.5m for congestion charge fees its vehicles dodged after it rigged emissions testing.
About 80,000 Volkswagens registered in London are affected by 'defeat devices', which were designed to trick emissions-testing software to appear more economical than they were.
VW admitted that 11 million cars worldwide were fitted with the devices, and researchers have now found similar systems in place in cars made by other manufacturers.
The £2.5m figure was calculated by Transport for London based on the number of VW owners claiming a congestion charge discount to which they were unwittingly not entitled.
"If you don't ask you don't get. I'm a champion for clean air, I'm a champion for London," said Sadiq Khan.
"Londoners, in good faith, bought these vehicles. They weren't clean. We've lost revenues from the congestion charge, they've got a case to answer."
In a statement to the Sunday Times, VW said: "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."
The cars would then enter a low-CO2 mode that would make emissions-testing systems register lower levels than would be found in the real world.