'A'-graded Euro 6 diesel models include the Audi A5 (161bhp 2.0-litre), Skoda Superb (148bhp 2.0-litre) and VW Golf SV (148bhp 2.0-litre), VW Passat (118bhp 1.6-litre), VW Scirocco (148bhp 2.0-litre) and VW Touran (108bhp 1.6-litre).
Other manufacturers with 'A' rated Euro 6 compliant petrols include: BMW, Citroën, Hyundai, Infiniti, Kia, Mercedes, Mini, Smart, Suzuki, Vauxhall and Volvo. BMW was the only non-VW Group manufacturer to score an 'A' rating with a diesel engine, with the 184bhp 2.0-litre unit powering the 3 Series.
However, the lowest rated Volkswagen car powered by a Euro 6 diesel - the 89bhp VW Polo powered by a 89bhp 1.4-litre engine - was rated only as an 'F', indicating it wouldn't meet any former Euro standards, and emits six to eight times the amount of NOx allowable in today's Euro 6 tests.
Furthermore, three vehicles powered by Euro 6 diesel engines have so far been given an 'H' rating - indicating that they are emitting high levels of NOx up to 12 times the legal standard for Euro 6 compliancy. Those are the Fiat 500X (118bhp 1.6-litre diesel), SsangYong Korando (176bhp 2.2-litre diesel) and Audi A8 (247bhp 3.0-litre diesel). The lowest-rated petrol-powered car on the list was the Ford Focus (123bhp 1.0-litre), which received an 'E' rating, meaning it only meets Euro 3 standards.
In line with many other manufacturers, many of the VW Group's Euro 5 diesel-engined cars were rated from 'E', to 'H', meaning they do not comply with any former Euro standard and emit roughly 12 times the Euro 6 limit of NOx. These engines are no longer on sale in new cars.
The full set of results is available here.
However, some manufacturers have questioned the veracity of the assessments. A spokesman for Fiat said: "This is a test devised by Emissions Analytics itself. We don't know how it was conducted or if it is repeatable. We are 100% behind real-world testing, but in the meantime we will work to regulations which provide us with consistent and repeatable tests. We do not think it is fair to be judged on this one result."
A Ford spokesman told Autocar: "We don't recognise this result. We would need to understand how the test was done and if it is repeatable."
Speaking to Autocar, Emissions Analytics boss Nick Molden said: "This has been brewing for a long time, but the short-term thing was dieselgate. It suddenly pushed emissions into the public domain, because it was only a specialist subject up until then. When dieselgate blew up we had more data than anyone to be able to prove the association between cars and high NOx emissions.
"Volkswagen come out as the head and shoulders winners out of this. They have this historical problem, but their current diesels are the cleanest on the market."
Chief Executive of the Society of Motor Manufacturers and Traders (SMMT) Mike Hawes said: "We can’t comment on results from non-official tests where the robustness or methodology is unclear. However, SMMT and the industry acknowledge the need for reform of the EU test process.
"We support the introduction next year of a more onerous lab test that better reflects real world driving, together with an on-road Real Driving Emissions (RDE) test that will measure not only NOx but other emissions, including soot particulates by both mass and number. This will be the world’s toughest emissions testing regime, with any model not meeting this stringent standard not being permitted for sale.”