Taxis and buses will automatically switch to “zero emission” electric mode on the country’s best-known shopping street and other roads where toxic diesel fumes are damaging people’s health.

New “geo-fencing” technology will ensure that when the hybrid vehicles cross boundaries into areas at risk of high air pollution, such as Oxford Street in London, they switch from diesel or petrol to electricity.

All new taxis in the capital from January 1, 2018, will have to be “zero emission capable” and there will be 1,700 hybrid buses on the road by 2016, under plans by Boris Johnson, the mayor of London, to avoid hundreds of millions of pounds in EU fines for failing to hit air quality targets.

An air pollution monitoring station in Oxford Street has recorded one of the world’s highest average levels of nitrogen dioxide, a pollutant from diesel exhausts linked to 7,000 premature deaths a year, according to King’s College London. The annual mean of 135 micrograms per cubic metre of air [mcg/m3] is more than three times the EU limit.

Matthew Pencharz, the mayor’s environment adviser, said it would not be practical to switch all buses and taxis to pure electric operation, partly as batteries do not have sufficient range.

“In the most polluted areas of town, the taxis would be in electric mode but when bombing down the M4 to Heathrow, they would have a little motor going,” he said. “With geo-fencing technology, when the vehicle crosses a particular line, it will go into electric mode. Some of our buses in future will also be doing this.”

“The technology can be responsive, so if one bit of town is more polluted than another, then the buses and taxis would switch to electric mode where the pollution was worse.” He said that “in due course” the technology could be fitted to private cars.

Yesterday, motoring organisations welcomed Mr Johnson’s decision to give drivers of existing diesel cars six years’ notice that they will be required to pay about £10 more a day to drive into the central London congestion charging zone from 2020.

“Very few cars enter central London so these measures will have more effect on the growing numbers of small businesses and service vehicles on whom London’s economy relies,” said Edmund King, the AA president. “They will have to plan ahead to change their vehicles if they are to stay in business.

“It is somewhat ironic that cars are banned from the most polluted street in London, Oxford Street. The vehicles that have most effect on air quality in London are buses, taxis and trucks.”

Ten million cars in Britain run on diesel engines — a third of the total.