Prime minister Theresa May has hinted that concessions may be made for diesel car owners after London Mayor Sadiq Khan confirmed proposals for new emission charges and reports that the government will introduce similar schemes in other cities.

She said: “Decisions will be taken when we produce that [air quality] plan. But I’m very conscious of the fact that past governments have encouraged people to buy diesel cars and we need to take that into account when we look at what we do in the future.”

The Mayor of London is already introducing a £10 T charge for the most polluting vehicles in October, and is proposing to introduce an Ultra Low Emission Zone (ULEZ) covering the current the same area as the existing congestion charging zone on April 8, 2019.

Petrol vehicles that don’t meet Euro 4 standards and diesel vehicles that do not meet Euro 6 standards will have to pay a ULEZ daily fee of £12.50 for cars, vans and motorbikes to drive in the zone. This will affect petrol cars more than 13 years old in 2019, and diesel cars more than 4 years old in 2019. The total cost, with the congestion charge added (during the times of day it is applicable), for motorists with these vehicles will be £24 a day.

Khan said: “The air in London is lethal and I will not stand by and do nothing. Today I’m announcing bold proposals which are critically needed to safeguard Londoners from our air quality health crisis.

“I am introducing a new T-Charge this October and subject to consultation, I want to introduce the Ultra Low Emission Zone in central London in April 2019. This alone will mean the capital has the toughest emission standard of any world city.”