Boris Johnson has been accused of taking a reckless approach to Londoners' health after refusing to appear before a parliamentary investigation into air pollution.
The environmental audit committee (EAC) today launched a new inquiry into air pollution following recent dangerous levels of air pollution experienced across the country.
However, sources at the committee said Johnson had refused to appear before them.
A spokesperson for the mayor would not say why Johnson would not appear, but insisted that one of his aides would be "likely" to attend at some point.
Opponents say the mayor is not taking the issue seriously, having previously dismissed air quality during the recent Saharan smog episode as "perfectly fine."
The EAC is calling for urgent action from the government and local authorities to tackle the problem of air pollution.
"Air pollution is thought to contribute to more deaths than passive smoking, traffic accidents or obesity, yet the UK is still breaching European safety limits nearly five years after EU fines were first threatened," committee chair Joan Walley said.
The mayor's refusal follows worldwide publicity for the recent so-called Saharan smog which sat over London for the best part of the week. Johnson dismissed the problem at the time, saying that he had cycled in the smog and found the air quality to be "perfectly fine".
Johnson's opponents said he was running scared of the committee.
"The Mayor has claimed to be doing all he can to improve air pollution in London, which many of us know to be nonsense," Green party London assembly member Jenny Jones said.
"His refusal to answer to the EAC is a clear indication that he also knows his claim is nonsense and he would be shown up as lackadaisical on an issue that blights the lives of Londoners, especially children and the sick."
Johnson's refusal to attend the committee's inquiry comes as campaigners revealed new findings showing large areas of London suffering under toxic levels of pollution.
Campaigners against Johnson's plans to construct a new four lane motorway crossing of the Thames in SE London, monitored pollution levels at 150 sites connected to the crossing earlier this year.
They found nitrogen dioxide levels up to two and a half times the legal level under EU regulations. In total, five sites recorded pollution levels at more than double the legal limit.
"Boris Johnson is backing dangerous plans for the Silvertown Tunnel rather than taking a stand against the lethal air pollution that blights our communities, and the traffic that causes it," Darryl Chamberlain, from No to Silvertown Tunnel said.
"The failure of Boris Johnson to address air pollution is damaging health and London’s economic development," Andrew Wood of Network for Clean Air added.
"The mayor of London needs to immediately appoint a commissioner for air quality with a task force to knock heads together, bring forward the start date of the proposed Ultra Low Emission Zone, and extend it to at least all the inner London boroughs – including Greenwich and Lewisham – which have harmful and unlawful levels of air pollution."
A spokesperson for the mayor said he was taking the problem of air pollution "very seriously" and was "driving the most ambitious and comprehensive package of pollution tackling measures in the world."
They insisted his plans for a new ultra low emission zone would be a "game changer" for air quality.
"The Mayor welcomes this enquiry. He will be submitting written evidence, and a representative from City Hall is likely to appear before the committee," they added.