Boris Johnson has announced plans to make all taxis in London zero emission by 2018.

As part of his commitment to introducing a new Ultra-Low Emission Zone to the capital, the mayor revealed that all newly-licensed cabs must have a function to allow them to produce absolutely no emissions from January 1st 2018. Drivers will be expected to activate it as they enter pollution blackspots.

Car manufacturers Nissan, Metrocab and London Taxi Company are thought to be developing the zero emission vehicles, with Transport for London (TfL) confident that the mayor's 2018 deadline will be easily met.

Some drivers are concerned, however, that the introduction of the new taxis will be too expensive. Garrett Emmerson, surface transport chief operating officer at TfL, outlined plans to consult with the industry and the Green Investment Bank "to provide assistance to cab drivers who want to be among the first to get behind the wheel of these cutting-edge vehicles."

London taxis are thought to contribute to around one-third of the toxic emissions in the most polluted areas of the capital.