London's long retreat from its Big Smoke epithet moved a step further yesterday, as Deputy Mayor Kit Malthouse unveiled a hydrogen-powered taxi. On the streets, the green machine releases nothing more noisome than water vapour, running off a tank of hydrogen coupled to a fuel cell. It's still only a prototype, but a small fleet should be carrying passengers in time for the Olympics. The cab, which can cover 250 miles on one tank and reach 80 mph, can be topped up from one of six refuelling stations currently being built around the capital. Image / Roll the Dice in the Londonist Flickr pool.