Drivers of older, more polluting vehicles now have to pay almost twice as much to drive into central London.
The £10 T-Charge, implemented by Mayor Sadiq Khan, mainly applies to diesel and petrol vehicles registered before 2006, has come into force.
It covers the same area as the existing congestion charge zone, bumping up the cost to £21.50 for those affected.
The measure is the latest attempt by Mr Khan to improve air quality in the capital and will affect 34,000 motorists a month.