One year since it began, the congestion charge has given Mayor Ken Livingstone reason to smile.

When he first proposed it and began his first term as Mayor in 2000, Mr Livingstone knew it was a gamble which could make or break his tenure at City Hall.

Speaking at a special press conference on the first anniversary of the £5 charge scheme on February 17, the mayor said it been successful beyond what he had hoped for.

He even allowed himself to get carried away.

"Overwhelmingly, this has transformed the experience of travelling and doing business in London," he said, when asked to rate the success of the first year of congestion charge.

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Mr Livingstone will know that there are major challenges for the scheme not least justifying his proposed westward extension of the zone and the outcry over the effect on central London business but it is hard not to see it as a personal triumph, which can only help his bid for re-election in June.

It has not raised as much revenue (about £70 million against projections of £180 million) as the Mayor and transport chiefs might have hoped, but there is no doubting its impact.

About 30,000 fewer cars, vans, and lorries enter the congestion charge zone every day, compared to levels before February 17 last year, and, overall, congestion is down by about a third.

Delays caused by traffic delays within the zone have been cut by 60 per cent, and average traffic speeds within the area have jumped. Most importantly, nearly 30,000 more passengers have taken to using the Mayor's beloved buses, with 560 new buses added to city routes. The firm running the charge, Capita, has been forced to recruit more staff and revamp their system after complaints of incorrect fines and administrative errors.

However, TfL expects these problems to disappear within the next few months.

With Mayoral and London Assembly elections just months away, Mr Livingstone knows he can use the introduction of the charge as formidable ammunition when talking about his record in office.

But his opponents may also see his close association with the charge as the best chance to attack him, especially given its failure to raise the expected revenue.

Conservative politicians, from Mayoral candidate Steve Norris to his counterparts on the London Assembly, such as Angie Bray, have decried the charge's effect on business - especially the smaller firms which rely on shoppers travelling into the city.

Their claims have been backed up by some surveys, which have shown considerable business disquiet about the charge.

The London Chamber of Commerce has called for the hours of charging, which run from 7am to 6.30pm, to be changed to encourage people to come into London outside of the morning and afternoon rush hours.

A Chamber survey found more than two-thirds of businesses felt trading conditions would be improved if the charge was stopped in the middle of the day, when congestion was lower.

But Mr Livingstone said the charge was only introduced because congestion in London had got to the point where rush hour' was lasting all day. He can also call on surveying by Transport for London, which found many businesses thought seasonal changes and general economic conditions had had more influence on their trade than the charge.

However, the Mayor has admitted that surveys on the effects of congestion charging, whatever their findings, can only be estimates after just one year of the scheme.

Given the Greens' obvious support for the charge, and the more qualified backing from Liberal Democrat mayoral hopeful Simon Hughes and Lib Dems on the GLA, opponents of the scheme may be looking to the Conservatives for leadership.

Along with their attempts to champion the cause of apparently beleaguered businesses in the charge zone, Tory politicians have also associated with residents on Kensington and Chelsea, where the charge zone may be extended. TfL has already begun consultation to this effect, and is looking at improving public transport in west London.

Residents in an extended zone would probably get the same discount to that offered to the 150,000 people who live in the current charge area. Shortly after the Mayoral election in June this year, Transport for London expects to have finished detailed consultation with various groups about extending the zone westward.

It could be that the Mayor who reads through these TfL documents will be the same one who introduced the original charge scheme.