Congestion... Emissions... What is it all about?
It's believed that thousands of motorists shelled out hundreds of pounds - some paid thousands - to convert their vehicles to run on liquefied petroleum gas, many with the intention of not paying the congestion charge, but their discount will be phased out by 2010.
That's the plan of Transport for London (TfL) who say the move would only affect a 'very small number of car owners'.
The announcement is part of plans to charge £25 for the highest polluting cars entering central London zone.
One reason for the change by TfL is that vehicles converted to use LPG can still use petrol, which is associated with CO2 emissions.