London is to take part in an environmental pilot scheme which will use emission-free buses costing £1m each.
Transport for London (TfL) is due to take delivery of the three hydrogen-powered vehicles later this year.
London is one of 10 cities which will trial the bus
They will come into service by the beginning of 2004, despite planning permission for a refuelling station being turned down.
London is one of 10 cities across Europe that is involved in the Clean Urban Transport for Europe (Cute) project, which will trial the new buses over the next two years.
The cutting-edge technology from Mercedes means that the exhaust emissions from the bus will actually be cleaner than London's air.
Mike Weston, from TfL, said: "London is the biggest operator of buses in Europe.
"We've put in a lot of effort over recent years to clean up the conventional diesel fleet.
"But this vehicle offers zero-emissions at the point of use and it's potentially a great improvement to the environment of London."
But their introduction will be delayed because a BP refilling station which was due to be established in Romford in east London, has been refused planning permission on safety grounds by Havering Council.
BP is set to appeal and a spokesman for the company said: "We have thousands of petrol stations selling LPG gas. Hydrogen isn't that different."