Four major car manufacturers were dragged into the Volkswagen diesel emissions scandal last night after Government-funded research revealed that their engines are emitting toxic fumes at up to seven times the legal limit.

British researchers tested hundreds of new diesel cars on UK roads and found that popular brands including BMW, Ford, Mazda and Mercedes, as well as Volkswagen and Audi, all emitted levels of nitrogen oxides (NOx) far higher than the limits required to pass European tests.

Last night, the researchers said the huge discrepancy between real-world diesel emissions and the legal limits set by the European Commission was ‘extremely concerning’ – and suggested that Volkswagen was not alone in finding ways to pass laboratory tests.

Ford is one of the manufacturers that has been dragged into the VW diesel emissions scandal (file photo)

Researchers found brands including Mercedes and Mazda emitted levels of nitrogen oxides above the legal limit

Ford’s new diesel engines emitted more NOx on average than all the other manufacturers tested in the sample

Dr James Tate, lecturer and researcher at the Institute for Transport Studies at Leeds University, said: ‘The surprising finding for us was that even the Volkswagen engines were polluting 35 per cent less than other comparable cars, suggesting all manufacturers have found their own ways of passing the laboratory tests.

‘We found small city diesel cars are emitting more than double-decker buses or fully laden 40-ton articulated lorries.

'This is big business for them [car manufacturers]. It lets them sell tax-friendly, powerful luxury cars with supposedly low emission levels and make higher profits.’

Dr Tate, whose work is funded by the Department for Environment, Food & Rural Affairs and local councils, has been monitoring diesel emissions on Britain’s roads for five years and has recorded more than one million cars.

His latest research looked at the new Euro Six category diesel engines – which were introduced in September last year. He measured 300 of the newest diesel cars at six locations in England and Scotland over 20 days during the summer.

He found that on average, none of the manufacturers met the Euro Six regulations that state the engines must not produce more than 0.08 grams of NOx per kilometre.

Mazda’s engines emitted the most on average (0.49 grams per km) – 6.1 times the Euro limit. One of its vehicles was found to discharge 1.1 grams per km – 13.75 times the limit. Mazda was bettered by BMW (0.45 grams), Mercedes (0.42 grams), Volkswagen (0.41 grams) and Audi (0.36 grams).

Dr Tate found that Ford’s new diesel engines emitted more NOx on average than all the other manufacturers tested, but in this case Dr Tate said more cars needed to be tested from the manufacturer due to a small sample size.

He also looked at Volkswagen’s EA189 engine – which the company was forced to admit last month had been fitted with ‘defeat devices’ that could sense when they were being tested in laboratory conditions and were programmed to emit less NOx.

Volkswagen's offending cars released 4.2 times the EU limit, while Mazda’s engines emitted 6.1 times the limit

Dr James Tate said that the research suggests other manufacturers have found ways to pass the tests

Volkswagen’s offending cars released 4.2 times the EU limit but other cars were worse – emitting 5.8 times the official standard.

Dr Tate said: ‘This research shows that building cars so they perform well in laboratory emissions tests but emit high amounts of NOx in real urban driving is an endemic practice across the industry.

'There is very little known about how the manufacturers conduct their tests because they take place behind closed doors.

‘What our tests do for the first time is show how much toxic fumes are really being emitted on British roads, and we have done that with a large sample size to give a much more accurate picture of the true scale of the problem.’

Rather than laboratory tests that don’t test cars on gradients or on corners, Dr Tate says testing cars in ‘real-world’ conditions gives a more accurate picture.

Testers used a Remote Sensing Device to record exhaust emissions as vehicles drove by on public roads. The tests are tightly controlled and widely used across the United States to monitor compliance of clean air rules.

The car’s number-plates were recorded and cross- referenced with the DVLA so researchers could see the make, model and engine size for each car. It is believed to be the most comprehensive picture yet of diesel fumes on Britain’s roads.

Greg Archer, of pressure group Transport and Environment, said: ‘These results show new diesel cars are not clean and VW’s cheating is the tip of the iceberg. Cars in Europe must be as clean and efficient on the road as they are in the laboratory. Europe’s paper tiger regulators must ensure that they are in the future.’

When contacted for comment, the manufacturers insisted that their engines met EU regulations and they did not cheat on tests.

A Government spokesman said: ‘We have been open about the difference between real-world and laboratory testing for diesel cars. We have been pushing at a European level for real driving emissions testing to ensure tests reflect vehicles’ actual performance on the road.’

British drivers to sue for £2.4bn compensation

By Simon Watkins and Mark Wood for The Mail On Sunday

Volkswagen owners caught up in the diesel emissions scandal could be in line for payouts of at least £2,000 each, say legal experts preparing to take on the firm in the courts.

The action could cost the German car giant £2.4 billion in the UK alone. The news will come as some comfort to owners of affected VW diesel vehicles, with the latest second-hand car valuations showing a worrying slump in resale values.

The respected Glass’s Guide said that between September 21 and 25, the value of second-hand VW diesels fell by 2 per cent. That compares with a fall of just 0.2 per cent between September 1 and 21 when reports about emission test cheating were only just starting to emerge.

Experts say that Volkswagen owners could be in line for payouts of at least £2,000 each following the scandal

Lawyers at Leigh Day said an average of about £2,000 per car was the minimum that VW would have to pay drivers.

The legal firm, which has been approached by almost 1,000 British car buyers and a number of businesses running fleets, wrote to VW in Germany last week to call for the company to agree a compensation scheme. They have not yet received a reply.

Partner Bozena Michalowska, who is spearheading the action, said: ‘The premium that they have put on these cars’ prices as “clean diesel” is about £1,000 more than the petrol versions of the same models. I think it is safe to say that on average, losses or compensation would be at least double this very conservative estimate.’

Ms Michalowska said the total compensation payable would be far higher once other factors were taken into account, including how the fix implemented by the car-maker affects the performance, running costs and tax payable.

VW has admitted 1.2 million cars sold in the UK were fitted with software that allowed the vehicles to hit targets for emissions by changing the way the engine operated when being tested. Eleven million cars worldwide are affected.

If a test case is proved, or VW agree to an out-of-court settlement, all owners who bought VW’s with the EA189 engine between 2009 and 2015 would be entitled to the payout.