London's traffic has defeated the Mayor

Why is the Mayor against single mothers, gays and ethnic minorities? What has he got against the poor and the elderly? Why does he not treat teachers as essential workers? None of these groups was on Tuesday's "honours list" of those exempted from his dread congestion charge.

Painful are the politics of patronage. This week Ken Livingstone listed those to be excused from paying £5 a day to drive into central London's new Control Zone, due in early 2003. They reflect those who have recently beaten a path to his door: public buses and coaches, taxis, licensed minicabs, nurses, firemen, the disabled, school and community vehicles, local government vehicles, the Royal Mail, cars carrying "confidential patient records", vehicles meeting "tough emission standards" and anyone residing inside the zone. This is an area roughly from Euston Road to the Elephant and from the Tower of London to Hyde Park/Victoria.

With each concession Mr Livingstone invites another. If firemen "travelling between stations", why not teachers or ministers of religion? Why does an expensive gas engine not contribute to congestion? Why the bias towards the public sector? Private cleaners are poor and tourist workers are vital to the London economy. The Mayor tried to charge delivery vans £15 a day but caved in after a fierce revolt by the white van drivers. He tried to extend the restriction period to 7.00 in the evening, but retreated to 6.30 when the theatres howled.

Nobody can complain that the Mayor has not consulted everyone. He has invited such a barrage of special pleading that he says he will spend Christmas digesting the result before deciding definitely to go ahead. Yet 200 monitoring cameras are already planned and the Driver and Vehicle Licensing Agency is standing by. Everyone wishing to drive into the central zone will have to register their number plates and either claim exemption or pay their £5 a day. Defy the law and the computer will issue a ticket. There will be a boom in "James Bond" rotating number plates.

I used to be mildly in favour of congestion charging. It puts a price on the road space which drivers occupy and thus on the wear and inconvenience they impose on others. The principle is fair and sound. We pay taxes to keep the Tube going, and pay to ride it. Drivers pay a licence and petrol tax, but get their road space free. We are told that the photographic monitor system is robust and works smoothly in Trondheim and Singapore, cities of which the Mayor apparently approves.

Yet the charge has been polluted by politics. The zone is ridiculously small. The City and West End are, it happens, the only places in urban Britain not seriously congested by traffic - except during road works. Traffic speeds are stable if not actually improving. Buses and taxis enjoy bus lanes, which a modest sum on policing could more rigorously enforce. The most effective control on traffic-has been a limit on the number and price of parking bays. Few people commute by car into the central area, and those who do are mostly rich and will pay anyway. Central London already has a congestion charge. It is called the £4-per-hour meter.

The hell is farther out, along the radials inside the North and South Circular roads. If you want to see serious congestion - and getting worse - visit the Mile End Road, the Great North Road, the Finchley Road, Fulham Palace Road, the Old Kent Road and the Highway. This is where car commuters need deterring and road space needs rationing. This is where Mr Livingstone's big revenue lies. His zone is too timid. It will also mean thousands of vehicles gluing up the perimeter just before 6pm, gunning their engines to roar over the boundary to grab any parking spaces left by the Mayor's favoured few.

Worse by far is that the projected revenue is plummeting. It was granted to the Mayor by central government over the Treasury's almost dead body, provided every penny went on transport. Early estimates were that, once the scheme was installed, revenue would be £230-£270 million a year against running costs of £30-£50 million. This would give the Mayor serious money to invest in buses and Tubes, though much of it was grabbed by Mr Livingstone in his election pledge of a flatrate 70p bus fare.

Since then, delighted lobbyists have been tumbling out of the Mayor's private office. At the last count he admitted that the profit will be nearer £125 million. Indeed, since the fixed cost of installing the system is estimated at £561 million, over the first five years it will take 90p to collect every £1. Nor is there any sign that Mr Livingstone has let up on his exemption bonanza. Excusing firemen and nurses, in circumstances impossible to police, will spark a stampede of other groups claiming similar blessing.

Is the game still worth the candle? The answer is moving towards no. Staff at Transport for London are reputedly enraged by the Mayor's constant capitulation to trade union and other lobbies. While revenues fall, costs are likely to rise. It is possible that Transport for London may itself advise against the charge when a final decision is made in February. Why infuriate drivers and hurl money at equipment manufacturers with so little to show for it?

There can be no realistic improvement in public transport come the launch date in 2003. Stephen Byers is still in charge of commuter trains and Tubes, and he will see to that.

This means trouble for Mr Livingstone, who faces re-election a year after the charge is due to begin. The policy was relatively popular two years ago. Indeed it was Mr Livingstone's one big manifesto idea. But to work it needed a flat rate across inner London, applied to all road users.

It needed a tough Mayor to make it work. It has found a weak one. As a means of political patronage, the congestion charge collapses. This time Mr Livingstone will have nobody to blame but himself.