London will see ‘green’ black cabs in time for 2012

Clean, near-silent electric motors will be used in the vehicles, which will have "fuel cell" batteries charged by converting hydrogen into electricity. The cabs will emit only water vapour.

The taxis, able to travel at up to 80mph, will be capable of running for a day without refuelling. Six specialist hydrogen filling stations will be constructed around the capital.

London Taxis International, Intelligent Energy and other partners are working together to produce the new cabs.

Deputy mayor Kit Malthouse said: "The black cab is a London icon but it is also a source of pollution. This prototype, which emits only water from its tailpipe, is a glimpse of how hydrogen technology could soon play a vital role in cleaning up air quality."