Drivers of the most polluting vehicles will have to pay almost double to enter the centre of London as of today.
The new £10 toxicity T-charge will be paid in addition to the congestion charge of £11.50, taking the total to £21.50, and covers the same area and operating times as the existing congestion charge zone.
It mainly applies to diesel and petrol vehicles registered before 2006 which do not meet the so-called "Euro 4" European directive to regulate vehicle emissions.
London Mayor Sadiq Khan has launched the T-charge to tackle London's air pollution and prepare the city for the introduction of the ultra-low emission zone, which he plans to introduce in April 2019.
He said: "As Mayor I am determined to take urgent action to help clean up London's lethal air. The shameful scale of the public health crisis London faces, with thousands of premature deaths caused by air pollution, must be addressed.
"Today marks a major milestone in this journey with the introduction of the T-charge to encourage motorists to ditch polluting, harmful vehicles.
"London now has the world's toughest emission standard, with older more polluting vehicles paying up to £21.50 a day to drive in the centre of the city. The T-charge is a stepping stone to the ultra-low emission zone, which could be introduced as early as 2019.
"This is the time to stand up and join the battle to clear the toxic air we are forced to breathe."
Friends of the Earth campaigner Jenny Bates says Mr Khan is "right to try to dissuade drivers bringing the oldest, dirtiest vehicles into central London" but warns it is "only one small step towards clean air".
She said: "We urgently need a programme of meaningful financial assistance to help drivers of the dirtiest vehicles switch to something cleaner, and bold policies to cut traffic over all."
Other cities across the UK are also planning to clamp down on polluting vehicles.
Earlier this month, Oxford City Council proposed a ban on petrol and diesel cars by 2020, and Leeds, Birmingham and Southampton are planning congestion charges of their own from 2019.
However, some people believe the new scheme will have huge knock-on effects and will penalise the poor disproportionately.
Rod McKenzie, director of policy at the Road Haulage Association, told Sky News: "It will have a big impact on business in London, the South East and by extension, the rest of the country, so everyone is affected by this.
"It will effectively outlaw and certainly tax all older vehicles and make business more expensive - it could even put some hauliers out of business."
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