The move is intended to deliver dramatic benefits in air quality and provide a major spur for the further development and mass take-up of zero and low emission vehicles.

Boris Johnson said: ‘Creating the world’s first big city ultra low emission zone has the potential to be a game changing moment in the quality of life of our great capital. My vision is a central zone where almost all the vehicles running during working hours are either zero or low emission. This would deliver incredible benefits in air quality and stimulate the delivery and mass use of low emission technology.’

In response, Friends of the Earth London campaigner Jenny Bates said that 2020 is far too late for an Ultra Low Emission Zone, with EU pollution limits due to be met by 2015.

She added: ‘Boris Johnson must take action by slashing traffic levels in the city through better public transport and encouraging more Londoners to get on their bikes.

‘The Mayor should also pull the plug on short-sighted plans for new Thames river crossings, which will simply add to the Capital's dangerously unhealthy poor air quality.’

Transport for London is now beginning work on preparing options for a public consultation on the Ultra Low Emission Zone.

Boris Johnson also announced changes to phase five of the Low Emission Zone, which is due to be introduced in 2015. This was intended to ensure that buses, coaches and HGVs driving into the Capital would be subject to emissions restriction but the Mayor has confirmed that they will now only apply to Transport for London’s fleet of buses. The move is expected to save around £350m in costs for businesses using vehicles that would have been affected by the changes.

The Mayor’s new package of measures also includes plans to increase the number of hybrid buses in the capital by 600 to over 1,600 by 2016, retiring less efficient buses and a study into potential zero-emission taxis.

The Mayor of London’s Environment Advisor, Matthew Pencharz, said: ‘The Mayor has put together a team that takes air quality seriously and that is why he has confirmed another £20m will be devoted to improving local air quality. He has also brought forward a package of measures that will deliver double the emissions savings originally forecast for phase five of the Low Emission Zone, whilst saving businesses already battling through a tough economic climate from a £350m bill.’