The western extension of the congestion charge should be preserved as a key element of the capital's efforts to fight climate change, according to Labour.

Speaking as the Mayor launched a five-week public consultation on the issue in Kensington High Street this morning, Val Shawcross, Labour's London Assembly transport spokeswoman, urged a rethink on the consultation.

Opponents of the scheme, introduced in February last year, are expected to call for the levy to be scrapped. They include thousands of traders and residents in Kensington & Chelsea and Hammersmith & Fulham, who say it is hurting business and failing to curb congestion.

But Ms Shawcross, who has the support of green groups, says those who want the extended congestion charge scrapped are wrong.

"The congestion charge is now much more than just a means to speed up central London traffic, it's a vital, forward-thinking weapon in the fight against climate change," she said. "Pollution and CO2 emissions don't recongnise postcodes and we all breathe the same air. He should be consulting everyone effected by the future of the charge."

The Mayor's supporters greeted today's consultation as the first step to unstitching an unpopular and unworkable policy.

it Malthouse, London Assembly member for West Central and a key adviser to the mayor, said: "Ken Livingstone forced it through despite a majority of residents and businesses being opposed. It was typical of the previous Mayor to ignore public opinion when it suited him, so I'm delighted Boris Johnson is genuinely seeking the public's view."

Charlie Mullins, managing director of Pimlico Plumbers, said: "Without a decent public transport system there is no point imposing the congestion charge in west London. In the current economy this additional cost would hit residents hard, espcially if there is no viable transport alternative."