Traffic jams in central London have increased year-on-year since the introduction of the congestion charge.
While there are 20% fewer cars compared with before the scheme went live in 2003, congestion has continually risen.
In its first year congestion was down 30% on pre-charge levels but in 2006 it was 8% lower than in 2002.
Mayor Ken Livingstone said extra congestion was due to a rise in roadworks but the Tories blamed his policy of extra bus lanes.
The congestion charge zone will be extended to Kensington and Chelsea in west London from 19 February.
Negative impact
Speaking at City Hall, Mr Livingstone said London would have ground to a halt without the congestion charge.
"Congestion is rising in London because of Mr Livingstone's transport policies"
He said estimates suggest traffic in the western extension would fall by up to 15% when the zone goes live.
He said utility firms such as Thames Water were responsible for a 191% rise in street works between 2004 and 2006.
"The planning and carrying out of street works is extremely chaotic, and is now having a negative impact on the effectiveness of the measures brought in to tackle congestion," he said.
However, the Conservative group said new bus lanes since 2004, including 10 lanes inside the zone, coupled with changes to traffic light timings have had a "huge impact" on traffic.
Angie Bray, of the London Assembly Conservatives, said: "Congestion is rising in London because of Mr Livingstone's transport policies.
"Fewer cars are using the roads yet congestion increases.
"The reasons? Poor planning and use of road space. Bus and cycle lanes in conjunction with re-phased traffic lights are making London travel slower."
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