It is part of a package of measures that Livingstone, who has made the environment a central plank of his tenure and who is facing a tough re-election battle in May, is bringing in to cut London's carbon emissions by 60 percent within 17 years.

"This package is very significant in global terms because the rest of the world is watching to see if we can deliver on this incredibly ambitious target of a 60 percent reduction by 2025," Mark Watts, Livingstone's climate chief, told Reuters.

London, which generates some seven percent of Britain's climate-warming carbon emissions, is in a vanguard of a group of 40 major cities worldwide pooling their knowledge to play their part in fighting climate change.

The city's plan is far more ambitious than legislation going through parliament to cut national emissions of the main greenhouse gas carbon dioxide by 60 percent by 2050.

The 25 pounds daily tax on vehicles in central London's Congestion Charge zone emitting 225 grammes of carbon dioxide per kilometre would apply in the same way as the normal eight pounds daily charge does to all but the cleanest cars.

But to force home the environmental point of a congestion scheme that initially had no green goal, the exemption granted to residents in the zone will be removed from drivers of the polluting four wheel drive and top end luxury cars.

That means that the owner of a gas-guzzler who chooses to drive in the zone every day will end up paying 6,500 pounds a year for the privilege.

"It is the first instance of real carbon pricing being applied to people's everyday existence," said Watts. "This is getting much closer to the idea of a personal carbon budget."

Livingstone is also expected next week to announce a major step forward in his campaign to get cars off London's roads with a boost for bicycling in and around the city.