You wouldn t find many people who would defend the right of people to dump their rubbish in the middle of the street. And any politician who said it was fine, would get pretty short shrift. Yet there is a well-financed lobby that argues exactly that princ

You wouldn't find many people who would defend the right of people to dump their rubbish in the middle of the street. And any politician who said it was fine, would get pretty short shrift.

Yet there is a well-financed lobby that argues exactly that principle when it comes to the future of our planet.

What's got the anti-green lobby exercised is the decision I took earlier this month to charge gas guzzlers £25 for driving into central London, with 100 per cent discounts for the greenest cars.

The CO2 charge is a radical measure based on the principle that we should put London first. 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 the £25 a day charge from October 27.

Technically, these are cars in Vehicle Excise Duty Band G. The charge has been set to reduce by two-thirds the number of trips by these heavily polluting cars. Such vehicles may be justifiable on a Scottish hill farm but it is completely unnecessary to take them into central London.

Approximately 33,000 gas-guzzling cars will be affected. At the same time, drivers of the lowest emitting vehicles, in bands A and B, such as hybrids and many smaller cars, will receive a 100 per cent discount while the majority of drivers will continue to pay the standard £8 a day.

Those who live within the congestion zone but choose to drive gas-guzzling cars will no longer be entitled to the 90 per cent resident's discount.

These steps come on top of London becoming, as of this month, the largest clean air zone - a 'low emission zone' - anywhere in the world, with the aim of reducing air pollution from lorries by introducing a charging and fining regime for the dirtiest vehicles.

Just as no one is permitted to throw his or her rubbish in the streets, so 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, will have to pay for the damage they inflict on the rest of us and the environment.

The luxury car company Porsche has responded by threatening a judicial review and setting up a website, www. porschejudicialreview.co.uk.

Green campaigners Friends of the Earth, Greenpeace and the Alliance Against Urban 4x4s have responded by launching a joint statement and petition at www.stopurban4x4s.org.uk.

Their campaign is supported by the Green Assembly member Jenny Jones and the Deputy Mayor of London Nicky Gavron. As Nicky argues, Londoners should be the ones who decide what measures are taken to combat climate change in their city, not a luxury car manufacturer, and they will have the chance to do that at the ballot box on May 1.

Nicky is right - the Tory candidate for mayor Boris Johnson strongly opposes the CO2 charge, describing it as 'poppycock.' My aim is to build on the progress London has made to improve our environment and tackle climate change. London is the only major city in the world to have achieved a shift from car use to public transport, through policies such as the congestion charge and big investment in the buses.

We are leading an international coalition of cities - the C40 group - to help the biggest urban areas develop ground-breaking policies against global warming. We have overseen an 83 per cent increase in cycling.

We should build on policies like these. The cash raised from the CO2 charge will be used to pay for a £500million investment programme in cycling and pedestrian improvements, combining priority measures such as 'super cycle-ways' with a Paris-style bike hire scheme and safe cycle zones. It will be the largest ever investment in cycling in London.

Boris Johnson opposed the Kyoto Treaty, first opposed the congestion charge and now wants to reduce the size of the zone, opposes the CO2 charge, and has attacked the Low Emission Zone as "the most punitive, draconian fining regime in the whole of Europe".

Seven in 10 Londoners think the most polluting cars should pay a higher congestion charge. But as Boris Johnson does not share this view, Londoners can decide on May 1 whether to go ahead with the scheme. If they want it, they can vote for me.

If they don't they can vote for Boris Johnson.

But what is absolutely clear to me is that Londoners should decide - not the Porsche motor manufacturer.