In-car electronic tags for the ‘tag and beacon’ congestion charge planned for central London from 2009 will be optional. Transport for London’s re-let, five-year management contract will also provide for satellite-based charging across Greater London in 2015 – within its two or three-year extension period. Any scheme would have to be inter-operable with a national charging system. Charges could vary from 15p to 60p per kilometre, depending on the level of congestion, time of day, or a vehicle’s emissions. The mayor has already asked TfL to investigate if the daily £8 charge could be hiked, to £20 or more, for heavy-polluting 4x4s.