MPs are launching a new inquiry into Government efforts to tackle air pollution which contributes to thousands of deaths a year.
The parliamentary Environmental Audit Committee (EAC) will examine what progress has been made to tackle poor air quality since it warned about the need for urgent action on pollution in a report in 2011.
Earlier this year, the European Commission launched legal action against the UK for its failure to reach targets - which should have been met by January 2010 - to cut excessive levels of air pollutant nitrogen dioxide, which mostly comes from traffic fumes.
Public Health England has warned that long-term exposure to air pollution led to around 25,000 deaths in England in 2010, while the kind of short-term peaks in pollution seen recently in parts of the UK can worsen asthma and affect lung function.
The EAC's chairwoman Joan Walley said: "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.
"The Environmental Audit Committee warned four years ago that an urgent policy response, greater public awareness and a shift in transport policy was required if air quality was to be improved.
"We will be examining what progress has been made by central and local government since then in removing the most polluting vehicles from the road and encouraging cleaner forms of transport."
The new inquiry will look at what progress has been made on issues including targets for air quality, support for local authorities to tackle pollution, low emissions zones and limiting emissions from vehicles.
It will also examine the role that could be played by new technologies and the scope for transport policies, such as public transport, cycling and walking, to cut air pollution.