A £1million taxpayer-funded Government test programme has confirmed VW Group were the only manufacturer to use 'defeat devices' to trick emissions tests but it also revealed that no car on the UK market could achieve legal limits for emissions in real world driving.
Both Euro5 and Euro6 cars emitted an average of six times the legal NOx limit in real world tests conducted by UK and German authorities.
Euro5 cars emitted 1,135mg/km compared to a legal limit of 180mg/km while Euro6 models hit 500mg/km (the legal limit is 80mg/km). Only three were within the upcoming 2019 tolerances and none met the standard of the 2021 laws, according to the Department for Transport report.
Roads minister Robert Goodwill said he's "disappointed" NOx results were as bad as they were and called on the industry to raise its game.
He added: "What's been disappointing is the level of non-compliance is higher than expected. It's like passing a driving test when you are being very careful but it's not the real world.
"Air quality is very important and the reason we have done this is to improve public health. I am disappointed the cars we are driving are not as clean as we all thought they might be."
A combined 93 different vehicle types were tested (37 in the UK) with a range of the best-selling diesel models selected - representing 50 per cent of all diesels on UK roads - including the Ford Focus, BMW 3 Series, Nissan Qashqai, Ford Mondeo and Vauxhall Astra.
Cars were sourced from car hire fleets with under 30,000 miles and fuelled with identical winter grade diesel. They were assessed in private labs using the official NEDC test and this was then replicated on track before cars were then taken through an emissions test out on the road based on the 2017 Real Driving Emissions regulations.
No defeat devices were uncovered on any models but there was evidence of temperature-based "gaming" strategies being used in the EGR system.
These systems are designed to reduce engine temperature and oxygen, which can stop NOx being produced. During the current NEDC test cycle these work at an optimum but in the real world, when ambient temperature is low or the engine is hot, illegally high levels of NOx are produced.
Manufacturers say this is to protect the engine from damage and the EGR strategy is within current laws. The new WLTP and RDE tests will remove the ability to manipulate tests in this way.
Goodwill added: "We weren't aware of the temperature situation and that's where manufacturers will need to address if they're are to comply with RDE."