London Mayor Ken Livingstone has announced that his congestion charge scheme is likely to be extended by the end of next year.
The boundaries of the zone, which currently covers an eight-and-a-half square mile area in central London, would grow to encompass the west London boroughs of Westminster and Kensington and Chelsea.
A separate inner ring road may be introduced in east London to take in Tower Hamlets, although the charge would be lower than the current £5 daily fee imposed on motorists between 7am and 6.30pm.
The mayor told the Financial Times of his plans to speed up the timetable for expanding the scheme.
But he said proposals would depend on the government progress on a national plan to use more advanced satellite technology.
He told the newspaper: "My guess is that the government will massively accelerate their timetable for a national strategy."
But the GMB union's London organiser Paul Kenny warned against extending the scheme into areas where people rely on their cars.
A survey showed that while up to 60% of people use public transport in parts of London, the figure is only 25% in Newcastle and Manchester and just 22% in Birmingham.
Mr Kenny said: "There is no point in considering penalising workers for using their cars if there are no real alternatives."
Mr Livingstone is unlikely to introduce any extension before the next mayoral elections in 2004.