A completely hybrid-powered fleet of buses would cut carbon emissions in the British capital by 200,000 tonnes each year, helping London to its target of cutting emissions by 20 percent by 2020, and 60 percent by 2050.

Hybrid-powered buses use a battery pack that is backed by a diesel engine.

Transport accounts for 20 percent of London's carbon emissions, with buses creating about five percent of all transport emissions.

"We take very seriously our role in cutting CO2 emissions and tackling climate change," Peter Hendy, London's transport commissioner was quoted as saying.

Transport for London, the body that deals with the capital's transport network, expects its all-green fleet to include, along with hybrid buses, biofuel-powered buses, and hydrogen-powered buses.

It cannot accelerate the introduction of the more environmentally-friendly vehicles, however, as lack of demand means manufacturers do not mass-produce them.

The decision follows a similar announcement in August by London's Metropolitan Police force that it would introduce increasing numbers of hydrogen-fuelled police cars to its fleet, to add to its more than 100 hybrid gas-electricity cars.

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