The carbon credits scheme is aimed at reducing greenhouse gas emissions. It is based on the polluter pays principle according to how much pollution they generate. The idea is that people are encouraged to pollute less, as it will cost them less in carbon taxes.
Drivers are charged for driving in the congestion charge zone in central London. The aim is to discourage drivers from using the zone during peak hours and use public transport instead, thereby reducing congestion, the time spent in queues, the pollution generated and the cost to the economy. The money generated is used to improve public transport, eg older London buses which generate more pollution have been removed from service.