The Vauxhall Astra produces far more harmful fumes on the road than in official tests.
Department of Transport figures show the car, which is built at the manufacturer’s Ellesmere Port plant, releases far more nitrogen oxide than previously believed.
Vauxhall have not broken any laws or regulations, or used any mechanism to hide emissions.
The government tested 37 of the UK’s most popular diesel cars to see how they performed in the ‘real world’, rather than in a laboratory.
Transport Secretary Patrick McLoughlin said: “Our tests published today have not detected evidence of manipulation of emissions lab tests as used by the VW Group by any other car manufacturer.
“The tests do show the widespread use of engine management systems to prevent engine damage which can lead to higher emissions in real world temperature conditions cooler than those in the approved lab test.
“Real world tests will be introduced next year to reduce harmful emissions, improve air quality and give consumers confidence in the performance of their cars.
“Following the Volkswagen emissions scandal the whole of the car industry must work hard to restore public trust by being transparent about the systems they employ and advancing plans for introducing cleaner engine technology."
The Astra, named European Car of the Year 2016, was tested under Euro 5 regulations for cars made after 1999.
It was found to release 1,686 mg/km of Nitrogen oxide (NOx) on the track, nine times beyond the lab limit of 180 mg/km.
Other Vauxhall models included in the testing were the Corsa and Insignia.
Tighter Euro 6 limits were brought in to test every car built after, but all 37 vehicles across the two criteria failed to come in under the limit on the track.
Officials are keen to stress they broke no laws or regulations because lab testing, not road testing, is currently the industry stanadard.
Results 'surprisingly different'
The report stated: “The emissions of NOx from the other tested vehicles… are surprisingly different when tested on a test-track or on-road under real driving conditions compared to those recorded in the laboratory.”
VW made headlines last year when it emerged the motoring giant had secretly installed software which detected when the car was undergoing a test.
The revelation that more diesel cars have failed emissions tests is likely to fuel demand for compensation from drivers.
In the UK car tax is based on how much carbon dioxide engines produce - with low-emission vehicles paying nothing at all. The scandal could also affect a car’s resale value.
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