It has emerged that Ken Livingstone and his transport chiefs deliberately over-played predictions of road chaos on the first day of the congestion charge.

Technology which could be used to set up a nationwide congestion charging scheme will be given a 12-month trial from this autumn, the Department for Transport announced yesterday.

The tests will establish whether a common system can work for all types of road to avoid the possibility of drivers having to understand varying procedures and equipment in different cities and regions.