Why I am declaring war on London's gas guzzlers

Cars with the highest greenhouse gas emissions, such as many so-called "Chelsea tractors", high-powered sports cars and other large luxury vehicles will face a charge of £25 a day from 27 October to drive in the central London congestion-charging zone. Technically, these are cars in Vehicle Excise Duty Band G.

The principle is simple. No one is permitted to throw his or her rubbish in the streets. No one should be allowed to emit pollution and carbon into the atmosphere from cars that are completely unnecessary in a city such as London.

This is the "polluter pays" principle. Those who choose to carry on driving vehicles that in some cases pump out four times the greenhouse-gas emissions of the lowest polluting vehicles, as well as senselessly and in some cases dangerously occupying road space, will have to pay for the damage they inflict on the rest of us and on the environment.

This charge has been set to reduce by two-thirds the number of trips by these heavily polluting cars. Transport accounts for one-fifth of London's greenhouse-gas emissions, the majority of which is produced by cars. Such vehicles may be justifiable for a Scottish hill farmer but it is completely unnecessary to bring them into central London with all the pollution and greenhouse- gas emissions they produce.

Approximately 33,000 gas-guzzling cars will be affected. The charge will raise £30-£50 million a year. This will in turn pay for all the improvements in cycling and walking in London I have announced this year. So the reduction in greenhouse-gas emissions will not only come from dissuading people from using highly polluting cars but from the improvements in other forms of transport.

At the same time, drivers of the lowest C02-emitting vehicles, those in Vehicle Excise Duty bands A and B, such as hybrids and many smaller ordinary cars, will receive a 100 per cent discount - while the majority of drivers will continue to pay the standard £8 a day charge.

Some have argued this will increase congestion inside the charging zone.

But that is unlikely. Only 3,000 band A and B cars, two per cent, drive into the congestion-charging zone each day at present. An increase in that will not make up for the very sharp fall in use of highly polluting cars that will result from the new charge - such gasguzzlers account for 17 per cent of the cars inside the zone.

Those who live within the congestion-charging zone but choose to drive gas-guzzling cars will no longer be entitled to the 90 per cent resident's discount. Residents have no choice about being in the zone - but everyone has a choice about whether or not to drive a gasguzzler, and if they choose to do so they should not receive a discount.

To give residents time to change their cars, annual resident's discount passes purchased before 27 October this year will be valid for a whole year.

For too long, city Londoners have complained about inappropriate, highly polluting cars - some more like tanks. It is particularly clear that many of these big cars are among the worst contributors to global warming.

Some people say this is about personal choice and people should be able to drive such cars if they wish. In fact if they wish to do this they should be paying for the damage they do to the environment. Others should not be forced to pick up the bill.

Seven in 10 Londoners think the most polluting cars should pay a higher congestion charge, according to a poll conducted by Ipsos Mori, and today's announcement delivers just that.

This is one of the three key tasks I have set as Mayor. The first two are that London's economy must be successful and that all Londoners must benefit from that success. But the third is that London's success must be sustainable - above all by improving our environment and tackling climate change.

Today's CO2 charge decision is therefore part of an overall strategy to improve London's environment and make sure London stays in the lead in tackling climate change.

This policy will sit alongside the London-wide Low Emission Zone, cutting pollution from lorries; a £500 million programme to transform cycling in London; support to enable Londoners save energy and cut fuel bills; a major programme to improve energy efficiency in public and commercial buildings; and a groundbreaking strategy to supply more of London's energy from renewable and decentralised sources.

While the extra revenue that will come from this charge will be beneficial for other forms of transport, I want to be clear that it is not primarily about raising income. I would be very happy if revenue fell because so few people were using such polluting cars. But any revenues that we do raise from the new C02 charge in its initial years will be invested in transport improvements that will further help to cut greenhouse-gas emissions. Combined, this could mean reductions in C02 emissions of up to 500,000 tonnes a year.

Some have argued against this £25 charge. Because it does not come into effect until October, Londoners will have the chance to vote on it at the Mayoral election. But I believe this is another key step forward in making London an environmentally sustainable city.

The eyes of the world will again be on London today. Already New York and others plan to follow London's lead with a congestion charge, and many others will consider moving straight to a CO2 charge if London's model is a success.

Climate change is the single biggest long-term threat to all our futures. Today's decision means that London will continue to be at the forefront of this struggle.