THE world's first hybrid engine double decker bus has been unveiled as part of London mayor Ken Livingstone's plans to cut pollution in the capital.

The environmentally friendly bus cuts carbon dioxide emissions by up to 40 per cent by using a combination of diesel and electric power.

The buses will eventually be introduced on all London routes with the aim of creating a 'green' fleet of red buses.

The £285,000 prototype was unveiled outside City Hall as the mayor announced that the first manufacturer to mass produce the vehicle would get the contract for all new buses in London.

"The first off the mark will get to corner the bus market until the others catch up with them - that should be a really attractive prospect," Mr Livingstone said.

"Hybrid vehicles can make a real contribution to a cleaner, greener public transport network for the capital. Bus manufacturers and operators now need to rise to this challenge to make this economically and financially feasible."

The double-decker hybrid will go into service at the end of the month on route 141 from Wood green to London Bridge.

There are currently six single-deck hybrid buses operating on route 360 from Elephant and Castle to Kensington.

A battery pack - which is charged by a diesel Euro IV engine - provides power to the wheels via an electric motor and when the vehicle brakes, energy which would normally be wasted, is also recycled and used to charge the battery.

Speaking at his weekly press conference, Mr Livingstone also joined a campaign by lobby group Friends of the Earth to call for a climate change bill requiring annual cuts in UK carbon dioxide emissions to be included in the Queen's speech on November 15.

Mr Livingstone and Friends of the Earth director Tony Juniper called for the Government to commit to reducing CO2 by 3 per cent each year.

The plea came a day after a report by Sir Nicholas Stern into the economic effects of climate change predicted a global depression if nothing was done.

"Climate change is the single biggest threat to the development of human civilization and as mayor it is my top priority for London," Mr Livingstone said.

"As the Stern review has shown this week, the future of our economy as well as our environment rests on taking action now rather than waiting for problems to unfold."

Mr Juniper said: "If the UK is serious about tackling climate change we need legislation to ensure that this happens."

The mayor said City Hall would re-evaluate all of its policies, including airport runway expansions, in light of the Stern report.