Plans to cut dangerous levels of air pollution from traffic in Scotland have been delayed by five years, putting the UK and Scottish governments at risk of multi-million-pound fines for breaching environmental law.

Glasgow is not expected to comply with air pollution safety limits until 2025, while Edinburgh, Aberdeen, Dundee and other conurbations won't meet the limits until 2020. The delays mean Scotland is deeply embroiled in a legal case that has already found the UK Government guilty of breaking air pollution law.

The delays have appalled environmentalists, who warn that thousands more people will suffer and die as a result. For the Scottish Government, they were "disappointing", while local authorities stressed the work they were doing to cut pollution.

Toxic particles from vehicle exhausts are blamed for killing at least 1600 people a year in Scotland, and 166,000 a year across Western Europe. They can trigger heart attacks, aggravate lung diseases and cause infections.

The UK agreed to an air pollution law that required levels of nitrogen dioxide gas in cities to be brought below safety limits by 2010. But as it had difficulties meeting this target, it applied for extensions until 2015.

In 2011 the Department for Environment, Food & Rural Affairs (Defra) accepted that Glasgow, along with other polluted urban areas in England, would not meet the target until 2020. This prompted the European Commission to launch a legal action against the UK in February.

But now, Defra has revealed that the situation has become far worse. Earlier this month it released a new set of "more pessimistic" official projections showing the Glasgow urban area is not expected to comply with pollution standards until 2025.

Another three large areas - Edinburgh, central Scotland and northeast Scotland - had been expected to comply with the extended deadline of 2015. But now, according to the new Defra projections, the air will not meet safety limits until 2020.

This means that the areas, which include Aberdeen, Dundee, Falkirk, Perth and other towns, become implicated in a second legal action being brought against the UK government by the environmental lawyers, ClientEarth.

Last year, this led to the UK Supreme Court declaring the UK Government in breach of its legal duty to meet nitrogen dioxide safety limits.

The UK court has now asked the European Court of Justice to rule on what remedial action it can compel the government to take.

Experts say the UK Government could end up being fined hundreds of thousands of pounds a day for the breaches. "Our case now has even wider significance for air quality throughout the UK," said ClientEarth's lawyer, Alan Andrews. "Unless the Government comes up with a plan to tackle pollution from road traffic, people will suffer from illegal levels of pollution for decades to come."

Friends of the Earth Scotland warned that Scotland was breaking European law on air pollution. "These delays see the prospect of clean air slipping over the horizon for people living in Scottish towns and cities," said the group's air pollution campaigner, Emilia Hanna.

She pointed out air pollution could stunt the development of children's lungs. "The Scottish Government has thus far proved itself unwilling to take the steps necessary to tackle this public health crisis."

The Scottish Government defended its role in trying to cut air pollution. "These revised projections from Defra are very disappointing as previous projections suggested that all parts of Scotland would comply with legal limits for nitrogen dioxide pollution from traffic within the next couple of years," said a spokeswoman.

She argued that Scotland had been working hard with local authorities and others to make "significant improvements" in air quality in recent years. "Our action plans set out the work being done to meet European Union standards in the shortest possible time."

The City of Edinburgh Council's environment convener, councillor Lesley Hinds, accepted that improving air quality was "a significant challenge for all major cities". The council was still working towards complying with the safety limits by 2015, she said. "We are acutely aware that there is still much to be done and although recent data shows that the situation does seem to be getting better in the capital, we are anything but complacent."

Glasgow City Council said it has two pilot projects to fit sensors to street lights to monitor air pollution levels. "The realtime information will help identify the reason for spikes such as taxis failing to turn their engines off at ranks, or buses sitting with their engines running at bus stops."

Aberdeen City Council said it was reducing pollution by managing traffic in the city centre, starting a car club and launching a fleet of hydrogen buses. A spokeswoman said: "The Aberdeen western peripheral route is also expected to improve air quality by diverting traffic from the city centre."

"Everyone can play their part by considering their travel habits and making small, meaningful changes where appropriate."

Craig Melville, convener of Dundee City Council's environment committee, pointed out that the northeast Scotland zone included eight local authorities and did not give compliance dates for individual cities.

"We are continuing to work towards improving local air quality through implementing the measures contained in our air quality action plan," he said.