The company says the latest examination of its large-scale test programme of passenger cars in Europe shows that the gap between the combined New European Driving Cycle figures and its real-world results has grown to 24% – up from the 16% average variance that it first recorded in 2012. 

As a result, the fuel economy motorists can expect from their new vehicles is hardly growing, just 2mpg over the last three years yet the official figures show a marked improvement.

The company added that while it is true that vehicles went through a phase of significant efficiency improvement in the past, these new results suggest progress in this area has now stalled. 

The company added that “any backlash against ‘dirty diesels’ may further work against greenhouse gas reductions if consumers switch back to the higher CO2 gasoline vehicles, despite the fact that the industry narrative and public perception about diesels may be lagging reality. We are seeing that the latest Euro 6 diesels are significantly lower in NOx and particulates. 

“The overall effect of these factors is potentially to constrain the UK’s ability to meet its greenhouse gas targets, and to cost the consumer more at the pump.”