The figure was calculated based upon the CO2 emissions of London’s 22,000 registered Hackney carriages (black cabs) but the figure would more than triple if London’s private hire vehicles, known commonly as “minicabs” also went electric.

The show’s study took into account the relative CO2emissions of the three most common Hackney carriages on the Capital’s roads – the TXI, TX II and TX4 cars built by manufacturer, Manganese Bronze – as well as the average mileage of the London cabbie.

Road transport is responsible for around 80% of airborne pollution in Central London, where air quality is at its worst, and black cabs account for 20% of that pollution. EcoVelocity event director, Giles Brown, said: 'Black cabs are one of the most common vehicles to see on London’s roads so it’s not surprising that they contribute a large proportion of the Capital’s pollution.'

Mayor of London, Boris Johnson, also announced in December last year a raft of "clean air" proposals, designed to improve London’s air quality. Rolling age limits (ten years for black cabs and 15 years for PHVs) will be introduced while, from 1 April 2012, all newly-licensed PHVs must be no more than five years old and meet the EU4 emissions standard. All newly-licensed black cabs must meet EU5 standards.

Taxi drivers will also be offered training in eco-driving, in order to promote more efficient driving techniques and reduce emissions, from next year. Eco-driving elements will also be added to the requirements before a new taxi driver is licensed.

Mr Brown added: 'It is exactly these types of initiatives that EcoVelocity is all about and what we are trying to further. Green motoring is here to stay.'