Petrol cars are emitting far higher levels of CO2 on the road than in official tests, despite the introduction of a new, tougher emissions regime. 

That’s according to testing firm Emissions Analytics, which carries out independent on-road assessments of vehicles. 

In response, the Society of Motor Manufacturers and Traders (SMMT) said it ‘strongly rejected’ the claim, which it described as ‘misleading’.

Emissions Analytics says that following the introduction of WLTP emissions testing, which replaced the old NEDC cycle, the average official CO2 emissions figure for petrol cars fell to 133g/km on an NEDC-equivalent basis – in contrast to the expected increase under the new regime. 

However, Emissions Analytics has found that the average real-world CO2 figure of the cars is in fact much higher, at 185g/km. 

The issue does not appear to be affecting diesel cars, for which the official figures are now very close to Emissions Analytics’s results.

The firm says it fears that the petrol discrepancy means optimisation of the lab-based WLTP test has already set in, with car makers adapting petrol vehicles to perform better in the test than they do on the road.

Emissions Analytics CEO Nick Molden said that such optimisation would make WLTP questionable in the same way as NEDC before it, affecting consumer confidence. 

Molden said: “While obtaining laboratory figures should be a useful way accurately to benchmark vehicles, there is a severe lack of validation and correlation with real-world use. 

“Granted, repeatability suffers when testing on the road, but it severely limits the ability of manufacturers to optimise for the test.” 

According to Emissions Analytics, the best solution is a certification programme that combined lab tests and on road validation. 

Molden said: “Until such a system is in place, there will be many more counterintuitive outcomes from an imperfect test regime caught in a switchover phase.

There is still fallout from Dieselgate and consumer trust needs to be built back up. The industry really needs to act now to avoid a Petrolgate.”

In response, SMMT chief executive Mike Hawes said: “We strongly reject these misleading claims, which at best betray a fundamental lack of understanding of the testing and regulatory process and at worst look like an attempt to unfairly discredit the industry for commercial gain.

“On-road testing of CO2 emissions can only ever provide a snap shot of how a vehicle is being driven and cannot be used as a comparison with official test values. 

“In fact, vehicle registration data shows there has been a significant rise in average CO2 values for both petrol and diesel models under WLTP, which is to be expected given the far more demanding test. Further, manufacturers are bound by regulations which specify how test results can be published.”

Hawes said that car manufacturers were fully aware of their responsibilities, and consumers could be assured that new cars were fully compliant with emissions regulations.

He added: “The new WLTP testing regime is the toughest in the world, more rigorous and complex than its predecessor and covering a wider range of driving behaviour to give fuel economy and emissions figures that better represent results achieved on the road.

“And because these figures are now provided not just for model ranges but individual vehicles, including optional extras, buyers have more detail to help them choose the most efficient car that best suits their needs.”