In October 2010, Volvo UK launched an app designed to encourage consumers to compare and contrast the impact of individual cars on air quality and human health.

Volvo wanted car buyers to think more carefully before making their choice (hopefully, of course, a Volvo) but the company also wanted to broaden the political debate. Too often, it felt, pollution was being measured exclusively in terms of CO2, ignoring the other mucky stuff cars also pump out. Emissions like carbon monoxide, oxides of nitrogen, sulphur and particulates.

Volvo UK's managing director Peter Rask, commissioned a promotional video and launched the app to great fanfare. Within six months the project had been withdrawn.

Watch Volvo's trailer for the app - which has since been withdrawn:

At a meeting in February 2011, attended by a host of manufacturers including Volkswagen, the Society of Motor Manufacturers and Traders told Volvo it wanted the app dropped immediately. Their logic was interesting.

Someone involved with the project told me "the SMMT said that the tests were so limited that you could not draw genuine conclusions about which cars were cleaner and which were dirtier. The published numbers couldn't be taken seriously. Everyone was gobsmacked, within weeks the app was dead in the water".

What even the MD of Volvo hadn't realised was that the tests for general toxic emissions weren't as thorough as those for carbon dioxide. Only one car is tested to set the value. Amazingly, after that, examples are only checked to see they are under the legal limit.

Put another way: the official emissions numbers recorded by the Vehicle Certification Agency (VCA) are based on a sample size of one and are therefore unreliable.

The VCA openly acknowledges the limitations of its emissions testing on its website, “unlike the CO2 and fuel consumption figures the figures for air quality pollutant emissions should not be used to directly compare different models of vehicle. The figures for these emissions are indicative rather than absolute, and emissions of them will vary within an acceptable range between individual production vehicles for each model.”

There was no cover-up here, no concealment but this is (yet another) example of the inadequacies of the current emissions testing regime.

Later on today the Transport Select Committee will question the MD of Volkswagen UK and the Chief Executive of the SMMT, as well as the Transport Minister, Patrick McLoughlin and the head of the Vehicle Certification Agency.

MPs will want to know if government has managed to establish whether other manufacturers sought to cheat their way through the testing regime in the way VW did.

Almost 1.2 million UK vehicles have been affected by the Volkswagen emissions scandal. Credit: Reuters

They will also want to know more about why there is a such a gap between the performance of cars on the road and in the lab test. VW broke the law but there is clearly plenty of rule-bending going on.

Ever since the VW scandal broke within the industry shutters have come down, wagons have been drawn together but a director at a company which tests cars on behalf of manufacturers told me that during tests, overseen by VCA, manufacturers routinely over-inflate tyres and adjust temperature (for example as high as 30 degrees) to ensure optimal performance.

Separately, but importantly, he points out that the "coast down curve" (a measure of the air resistance of car on the road) which is submitted by the manufacturer as part of the test is calculated by the manufacturers on a test track out of sight of the VCA.

It is apparently common practice to remove spare tyres, windscreen wipers, wing mirrors and tape up radiator grills to reduce drag. Road surfaces are mirror-smooth and graded to reduce resistance.

Once again there is nothing in the rules that prevents this sort of practice, in fact anyone not doing so arguably cedes a competitive advantage to their rivals.

In public, manufacturers deny this sort of shenanigans goes on. It should be an interesting session.

The chief executive of the SMMT, Mike Hawes, spoke at the National Air Quality Conference recently.

He said:

"For the record, vehicle manufacturers cannot and do not:

• Remove mirrors, seats, windscreen wipers – or indeed any other components

• Disconnect the alternator

• Tape over panel gaps

• Use special oils and lubricants that are not in production vehicles

• Fit special tyres or overinflate them

• Alter wheel alignment

• Use higher gears than in normal use."