London Mayor Ken Livingstone said he could extend the congestion charge zone by the end of next year.
Livingstone plans to enlarge the zone to take in the boroughs of Westminster and Kensington & Chelsea, and later to include Tower Hamlets in the east.
However, Livingstone's plans depend on him still being Mayor. He comes up for re-election in June 2004.
The Government is investigating a national plan using advanced satellite technology that would monitor vehicle movements in and out of congested areas and deliver a charging bill to the motorist, depending on the length of time spent in a zone and the time of day the trip was made.