The Volkswagen Group has been found to be the only manufacturer to fit devices designed to defeat the approved emissions test, Government research shows.

The six-month programme involved 56 vehicle types tested in Germany and 37 models tested in the UK by the Vehicle Certification Agency, on behalf of the Department for Transport.

Both processes involved using portable emissions measurement systems to compare laboratory results with those from a test track and typical road use.

Vehicles were sourced from car hire fleets and had completed no more than 30,000 miles. They were checked for defects before being included in the programme.

Commenting on confirmation that no defeat devices were found on non-VW Group vehicles, transport minister Robert Goodwill said: "This finding is a significant step forward in assuring drivers that the serious breach of trust committed by Volkswagen is not more prevalent."

However, the tests provided further evidence that nitrogen oxide (NOx) emissions are higher in real-world conditions and on the test track than they are in laboratory conditions.

While this was the case for all vehicles - chosen to represent a 75% spread of the 70 most popular diesel models of recent years - results varied significantly between different makes and models.

The report stated that existing lab tests designed to ensure emission limits are met have been shown to be inadequate and this is why the UK has secured a tough new Europe-wide ‘real driving emissions’ test.

From next year, vehicles will have to meet emissions limits in real driving conditions across a wide range of typical operating temperatures.

This aims improve consumer confidence in manufacturers.

"The UK will be working to ensure that the new rules for real driving emissions and type approval are robust, deliver the expected outcomes and that manufacturers behave consistently," the report added.