Here are some of the key questions answered about the scheme.
What is the Ultra Low Emission Zone (Ulez)?
It is an area in London where drivers of older, more polluting vehicles are charged a daily fee.
What has changed?
It previously only covered parts of central London, but on Monday it became 18 times larger.
What are the new boundaries?
The Ulez has been extended to include all areas within the North and South Circular roads.
Who has done this and why?
The change has been implemented by London mayor Sadiq Khan in an attempt to improve air quality in the capital.
What is the charge for non-compliant vehicles?
The daily fee is £12.50 for cars, motorcycles and vans up to 3.5 tonnes.
Heavier vehicles, including lorries, buses and coaches, are charged £100.
When do charges apply?
All day, every day of the year except on Christmas Day.
How quickly do I have to pay?
You have until midnight on the third day after the journey.
How do I do it?
You can pay online through TfL’s website, using the Pay to Drive in London app, or by phone.
Drivers also have the option of setting up automatic billing so they are charged monthly.
What happens if I do not pay?
You could be handed a Penalty Charge Notice for £160, reduced to £80 if paid within a fortnight.
What vehicles are affected?
It depends how much nitrogen dioxide it emits, which is generally linked to its age.
For diesel cars, most of those that meet the minimum standard were first registered after September 2015.
Compliant petrol cars are typically those registered after 2005.
How can I check the status of my vehicle?
Transport for London is urging people to use its online checker by visiting www.tfl.gov.uk/modes/driving/check-your-vehicle.
Where does the money go?
TfL says the cash it receives from the Ulez is reinvested into improving London’s transport network and to improve air quality.
It insists “we don’t make a profit” from the scheme.