The enlargement of London's congestion charge zone moved a step closer today when the capital's mayor, Ken Livingstone, unveiled plans to extend it westward to include Chelsea and Knightsbridge.

Mr Livingstone described the expansion as the "logical next step" but conceded that further consultation was necessary before the final go-ahead as the plan was "clearly controversial".

A charge of £5 for motorists entering central London on weekdays was introduced last year.

The scheme polarised Londoners, but the introduction went smoothly and many have hailed the charges as something for cities to emulate around the world.

Mr Livingstone, speaking upon the publication of his revised transport strategy, promised further investigation into proposals to extend the "c-charge" in 2006.

While promising consultation, he indicated he would not be totally governed by its results, believing that such exercises tended to lean towards those who had objections.

This drew fire from Angie Bray, congestion charge spokesperson for the Tories on the London assembly, who also represents the area affected by the expansion. She said: "The mayor's consultation has been a sham all along. This is a slap in the face to all of those residents who took the trouble to register their opposition to this scheme."

There has been opposition to a westward expansion from residents and businesses. Ms Bray said: "A two-thirds majority of residents against expansion is no small margin and yet the mayor has totally ignored their views. This is a sign of arrogance of the highest degree from a mayor that claims to be a man of the people."

But Mr Livingstone said: "Prior to the introduction of the existing scheme people were opposed to it, but since its launch there has been a marked increase in acceptance, with most people supportive of it."

He promised to address concerns about the operation of charging and stressed that if the extension to does go ahead, it could not be operational before late 2006 at the earliest.

The proposed new congestion area would be an area broadly bounded by Harrow Road, Scrubs Lane, West Cross Route, the Earls Court one-way system and Chelsea Embankment.

Mr Livingstone said: "An extension in this area is a logical next step for congestion charging, but I accept that the draft proposals may have appeared to be too prescriptive."

He admitted more investigation was needed on the proposed new northern and western boundaries. Also, there was a case for bringing the end of charging in the extended zone forward to 6pm to assist business, he said. Charges currently apply until 6.30pm in the central area.

But Ms Bray said that almost 85% of businesses based within the proposed new zone were against extending. She said: "This is because they have seen the serious trouble businesses in the current zone are already experiencing."

The AA said that talk of an extension was premature. An AA spokeswoman said: "It is a high-risk strategy that is going to affect loads more residents and it is going to be more confusing than the current scheme.

"It will also prove to be unpopular. According to our findings, two thirds of people in the area don't want the scheme. In addition, Transport for London believes the extension will lose money for at least 10 years."