London Olympics 2012: Air quality row may hit games
The UK is set to miss EU targets on air quality, government documents say - which may mean a legal row just before the London Olympic Games.
The targets should be met by 2015.
But the Department for Environment, Food and Rural Affairs (Defra) has admitted many cities will not meet them before 2020, while meeting London's targets could be as late as 2025.
If the European Commission is not satisfied by these plans, it could launch infringement action next year.
The government must submit its proposals in September, and the commission then has nine months to evaluate them.
If it decides to take action against the UK, that could begin next June - a month before the Olympics open.
"The 2025 date [for London] was a bit of a surprise," said Alan Andrews, an air pollution specialist with the environmental law organisation ClientEarth.
"We knew meeting the 2015 target was going to be difficult, but I thought they'd give it a go - but they seem to have thrown their hands up and said 'it's too difficult'."
Pollution was one of the issues that brought criticism - largely from the West - of the Beijing Olympics in 2008, when transport and industry had to be restricted in order to bring pollutants down to acceptable levels.
The EU restricts emissions of nitrogen dioxide (NO2) and other pollutants because of their health impacts.
Existing levels are thought to cause about 3,000 people to die prematurely each year.
The targets were originally due to be met in 2010.
Many EU countries, including the UK, had problems meeting this deadline, and were granted extensions until 2015.
The Defra documents point out that for most of the country, levels are within the EU limits.
But 40 places in the country - mainly heavily urban areas - are not compliant, and may not be so until 2020 - or 2025 for Greater London.
The government also published details of a number of initiatives aimed at curbing emissions.
These include financial incentives for switching haulage from road to rail, research on how retailers could deliver goods outside peak times, and differential pricing for vehicles emitting lower levels of pollutants.
And the majority of non-compliant zones, it says, will meet the NO2 targets by 2015 given the measures being put forward.
A government spokesman also told BBC News that it did not expect action from the the commission "if it is satisfied the UK is doing all it can to meet the NO2 limit values as soon as possible".
"The draft plans published today represent our best efforts," he said.
Kulveer Ranger, director of environment for London Mayor Boris Johnson, said: "The Mayor has initiated a robust range of short and long term sustainable measures to reduce pollution in the capital to confront the legacy of poor air quality he inherited.
"This includes the first ever age limit for black cabs, record investment into cycling, cleaner buses, and tougher standards for the London Low Emission Zone, the largest zone of its type in the world."
However, Mr Johnson scrapped part of London's congestion charge zone earlier this year, which has resulted in a higher number of cars travelling at lower speeds than previously - although Transport for London says there has been little impact on air quality.
EU rules aimed at lowering vehicle emissions through technical changes have not brought anticipated reductions.
The gradual switch from petrol to diesel engines has not helped; and it has recently become apparent that the tests vehicles have to go through to determine their NO2 emissions do not represent the realities of urban driving.
But critics say the current and previous UK governments have relied too much on technology, and failed to do anything else to bring levels down - which is why London's NO2 levels are among the highest of any European capital.
"We need a nationwide framework for low emission zones, and we need to push ahead with alternative fuels - such as electric vehicles, hydrogen and natural gas," said Mr Andrews.
"But we can't only look at technical fixes - we need to be reducing traffic volumes."