Boris Johnson has called for all older diesel cars to be scrapped because their fumes harm Brits' health.
The London mayor wants the Government to pay the owners between £1000 and £2000 ($2000-$4000) in a national scrappage scheme.
He said millions were unfairly "seduced" into buying diesel by being told it was greener.
"I feel very sorry for them,' Johnson told the Commons Environmental Audit Committee.
"This has been a massive failure of public policy.
"Millions were told they were doing the right thing, the clean thing, the environmentally friendly thing, by buying a diesel.They feel very hacked off now they're told they are more polluting."