Anybody old enough to remember those Nuclear-Free zones of the 1980s? Looney left local councils declared a small area of a city as a ‘nuclear-free zone’, to demonstrate their right-on credentials.

Lots of people scoffed. Would the Soviet Union, if it decided to nuke the UK, carefully avoid flattening its fellow communists? Would radiation fallout not drift across into the most ideologically-sound streets?

Well, the Nuclear-Free zone is back, but this time it’s called the London Congestion Charge.

Today, Mayor Ken Livingstone announced what has been threatened for the last two years. That cars in Band G (that’s emissions of 225g/km and above) would be charged £25 per day to move in the zone. And if you live in the zone, the 90 percent residents discount will be dropped, too.

Still, if you have a car in the A and B bands, entrance will now be free, instead of £8. There again, if too many of us buy these cars –such as Mini Cooper diesels - Band B will likely be charged at £4 per day from 2010.

The new regime comes in on 27 October and Red Ken says: "The CO2 emissions from the most high powered 4x4s and sports cars can be up to four times as great of those of the least polluting cars. The CO2 charge will encourage people to switch to cleaner vehicles or public transport and ensure that those who choose to carry on driving the most polluting vehicles help pay for the environmental damage they cause."

The C-Charge zone is a tiny – though influential – area in the middle of a very large city. How can virtually banning larger-engined vehicles make any difference at all to real-world CO2 levels? And petrol engines are far from 'polluting'. In fact, they are much cleaner than diesel engines - especially those engines in London's worn-out black cabs.

But why does micro-CO2 reduction make such a difference in Chelsea and Kensington, and yet there’s no need for a charge a few hundred feet away in North London, or in the East End? The only possible conclusion is that London is sliding back into the bad old days of political posturing, with politicians trying to impress their fellow ideologues across the world rather than actually achieve anything useful.

Red Ken may be pleased that, at the fag end of his political career, he has temporarily stopped Porsches moving in central London during the day. But the rest of us can see this move for what it is: the last thrashings of a bedsit revolutionary.