The North Circular, which carries more than 60,000 vehicles a day, has the worst traffic fumes of any road in London, according to official emissions figures released under freedom of information legislation.

Exhaust emissions data held by Transport for London show that a stretch of the road near Walthamstow ranked highest for four of the five most dangerous air pollutants, including benzene, nitrogen oxides (NOx) and fine particles of unburned carbon called PM10s and PM2.5s.

Four of the capital's five worst roads for air pollution pass through some of the poorest areas of east London, including the A13 in Tower Hamlets and the Dartford crossing (A282) near Thurrock.

Oxford Street and Piccadilly in central London ranked in the worst 15 roads, due to the large number of buses and taxis. In west London and the wealthy stockbroker belt the air is cleaner, with roads in Weybridge, East Molesey and Esher the cleanest of the 41,713 recorded last year.

Air pollution from traffic is linked to strokes, heart and respiratory diseases as well as some cancers and asthma. About 4,300 premature deaths a year are attributable to air pollution, according to studies for the London mayor, Boris Johnson.

Pollution watchdog groups accused the government of trying to conceal the seriousness of traffic pollution. According to the data, which does not include pollution from brakes and tyres, Marylebone Road in the city centre ranked 1,074th for NOx levels and 1,126th for particulate pollution, yet was consistently said by government to be the worst in the capital.

Jenny Jones, a Green party London Assembly member, said: "[The government] has been fooling the EC by understating how bad pollution is on many roads. Oxford Street and some local shopping areas appear to be more polluted than Marylebone Road, but the government seems reluctant to measure air pollution where it could be having the biggest impact on people's health."

The mayor's office said: "Strenuous efforts are being made to improve air quality in the capital. The mayor has tightened regulations on vehicles in the low emission zone, one of many changes that have resulted in emissions of dangerous particulates (PM10) falling by 15% and of oxides of nitrogen by 20%."

The data raises new questions for Johnson's plans for two new east London river crossings, because the figures show that any new bridges or tunnels built would increase the health risks in areas already among the most polluted in the capital.

London has the highest levels of nitrogen dioxide (NO2) of any capital city in Europe. Fifteen other British cities and regions – including Manchester, Birmingham and Glasgow – are heavily polluted by traffic and, according to the government, are not going to meet the legal requirements for lowering emissions for at least seven years.

Last month the supreme court ruled that Britain was in breach of EU law on NO2 emissions from exhausts. The case will now be heard in the European court of justice, and the government could face stiff fines.

Parliament's environmental audit committee estimates that outdoor air pollution causes 29,000 deaths a year in the UK, compared with fewer than 2,000 a year caused by road traffic accidents.

Simon Birkett, director of Clean Air in London, which applied for the data, called on the government to ban diesel vehicles in the worst affected areas. "Hundreds of thousands of people are being gassed and showered in deadly particles from taxis and diesel vehicles," he said. "All diesel vehicles from the most polluted parts of London should be banned by 2020."

Jenny Bates, Friends of the Earth's air pollution spokesperson, said: "This shows that urgent and bold action is needed to tackle the deadly air pollution problem in areas where EU legal limits are not being met. Local people have been suffering premature death and ill health for too long. Traffic levels must be cut by making walking and cycling."

safer and improving public transport."