Zero Emission Fuel Cell Hybrid Taxi: Carbon-free cab even south of the river

You'll never guess who we had in our cab this morning. It was Crave, at London's City Hall to see the new Zero Emission Fuel Cell Hybrid Taxi, a crud-free hackney that runs on hydrogen and produces no dirty carbon emissions.

The classic London double-decker recently had a climate-friendly makeover, so it's time for the iconic black cab to join in. The success of the hybrid vehicle depends on take-up by cabbies, but they may not have much choice: London mayor Boris Johnson has committed to see all London taxis operating with zero emissions from their tail-pipes by 2020. The first elements of a hydrogen infrastructure in place by 2012 -- whether there will be some sort of subsidy for the hybrid vehicles is as yet unknown.

Hydrogen allows for faster fuelling and gives a longer range than electricity: a 5-minute pit stop will run a cab 250 miles, or a full day's fares, even including airport runs. The disadvantage is that hydrogen doesn't yet have an infrastructure, unlike electricity. Storage and pumping stations are required, whereas you can just plug your 'leccy car into any mains socket. But infrastructure is less of a problem for a city taxi fleet than consumer vehicles, because they're concentrated in one area and already work on the principle of returning to base.

As well as the range and charging advantages, the hybrid hydrogen system is near-silent, more efficient from a cold start, and can hit 80mph. We should note however that, like electricity, hydrogen only offers zero emissions from the exhaust pipe of the vehicle itself. Carbon emissions are emitted during the production process, varying according to how the electricity and hydrogen is produced.

Crave visited the mayor's gaff in the shadow of Tower Bridge to witness the unveiling of the Zero Emission Fuel Cell Hybrid taxi. Flag us down, jump in and click 'Continue' as we race through photos of the cab to find out how it works. Follow that cab!