The ultra-low emission zone (Ulez) is being introduced in London.
Here the Press Association looks at some of the key questions around the scheme.
What is it?
The Ulez is a way of charging vehicles which emit the most nitrogen oxide for entering parts of London.
When is it starting?
The daily charge begins on Monday and will run from midnight to midnight every day.
Where is it happening?
The scheme will initially be within the same area as the congestion charging zone, before being expanded to within the North and South Circular roads from October 2021.
What vehicles are included?
All vehicles will be affected apart from black taxis.
How much will it cost to enter the zone with an older vehicle?
It will cost £12.50 for most vehicle types, including cars, motorcycles and vans. Heavier vehicles such as lorries, buses and coaches will be liable for a £100 charge.
How can I avoid the charge?
To be exempt from the Ulez charge, petrol cars, vans and minibuses must meet the Euro 4 emissions standard and diesels must meet Euro 6.
That means the oldest car that can be driven in central London without paying will roughly be a four-year-old diesel model or a 13-year-old petrol model.
What if I don’t know my vehicle’s emissions standard?
Drivers can check whether their vehicle is liable for a charge by entering its registration on the Transport for London website.
Why is Ulez being introduced?
London mayor Sadiq Khan says the scheme will improve the capital’s air quality, which he says is responsible for thousands of premature deaths and other serious conditions.
Has there been any opposition to the scheme?
Conservatives on the London Assembly claim Mr Khan’s decision to introduce the scheme earlier than planned could catch out some motorists – particularly those from the poorest households – who have not already upgraded their vehicle to a newer model.
They also warn that expanding the zone to the whole of inner London will not effectively tackle pollution and will affect people and businesses in areas with low pollution.