Porsche, Bozza and Paddick

The curious alliance between the Tory and Lib Dem candidates and the maker of some rather polluting

It was always going to cause a stir. The new emissions-based Congestion Charge (the 'CO2 Charge') was confirmed by Ken Livingstone at a press conference at City Hall last week. I was there to witness him signing the order to bring in the new scheme, which means that, from 27 October, the most polluting band G cars (emitting more than 225 grams of carbon dioxide per kilometre) will pay £25 per day to come into the central London C-Charge zone. Meanwhile, the cleanest cars in bands A and B (less than 120 g/km) will get a 100% discount, at least for a while.

Acknowledging the part my campaign group the Alliance Against Urban 4x4s played in delivering public support for this measure, Ken Livingstone tried to hand me the pen used to sign the order as a souvenir. Unfortunately, the pen in question turned out to be a birthday present belonging to a member of GLA staff, so I wasn't after all able to place it in our campaign museum (along with our first spoof parking ticket and our collage of sweary emails from petrolheads) but it was a nice gesture.

Despite the long-overdue need for real financial incentives for cleaner cars, it is election time, so the announcement immediately prompted knee-jerk attacks from the other Mayoral candidates. Not only that, but gas-guzzler manufacturer Porsche has since threatened a legal challenge and both candidates have used this as an excuse to criticise the scheme again. Boris Johnson said he “understood where Porsche was coming from", while Brian Paddick added, "Porsche have a point."

I'm not worried by the legal threat at all. I don't see how a classic case of applying the 'polluter pays' principle could be classed as discrimination, especially since Porsche could easily make vehicles under 225 g/km but simply choose not to. And people will still be free to carry on driving big, polluting cars in central London; all the new charge means is that they will have to pay more for the extra cost of the pollution that they create. It all seems perfectly fair to me.

Legal experts agree that Porsche's threat is unlikely to come to much in the end. Barrister Nick Armstrong told the Guardian that 'unfairness' to Porsche owners was unlikely to wash with the High Court, saying, "On the face of it is difficult to see how Livingstone's decision falls outside the range of reasonable responses."

Reading through the newspapers on this, it's sometimes hard to tell the complainers from the proponents of the scheme. While the head of Porsche UK (against) is actually complaining when he says that the new charge is, "a green tax for those who own certain cars in London,” Ken Livingstone (in favour) is all for it when he says it would, “ensure that those who choose to carry on driving the most polluting vehicles help pay for the environmental damage they cause.”

Similarly, while Tony Juniper of Friends of the Earth (in favour) says, “It would be more appropriate for Porsche to put its effort into making a new generation of much less polluting vehicles,” Brian Paddick (against) says much the same with, “Manufacturers are already modifying their cars to come in just under the CO2 threshold.” Yes Brian, that's the very idea and, if they do, it will represent a real advance. The difference between the 348 g/km of CO2 chucked into the atmosphere by the Porsche Cayenne and the 225 g/km that would bring it under the threshold is significant, even if 225g/km is still too high for a truly sensible car.

I find Paddick's strident opposition to this measure the most bizarre development here. After all, while on the London Assembly, one of the earliest proponents of this measure was Lib Dem MP Lynne Featherstone. In fact, a lot of his policy-making is starting to develop a back-of-an-envelope feel, especially on green issues. His campaign has come up with a long, rambling list of alternative ways of cleaning up London's cars including (weirdly) off-setting schemes and a self-defeatingly large £10 congestion charge zone extending right up to the M25.

What's not in doubt is that this is definitely an election issue so, if some people don't like the idea, they can of course vote for one of its opponents in May, rather than for me or Ken Livingstone.

Having argued for these changes for four years with the Alliance Against Urban 4x4s, and having looked into almost every detail of the Congestion Charge for our report to TfL in 2006, I am very happy with the resulting scheme. My one quibble is that, at the bottom end, there is no confirmed date for when the zero-charge band will be tightened. That's why, in my response to the recent consultation, I proposed making it clear now how the emission bands at both the top and bottom ends would be strengthened over time.

However, while I am being constructive, both Johnson and Paddick aren't helping themselves or their campaigns with their attacks. When you find yourself arguing on the side of a petulant car company against the interests of ordinary Londoners, you should realise you've taken opposition for opposition's sake too far.