The system of testing cars to measure fuel economy and CO2 emissions is utterly discredited. This report analyses the gap between test results and real-world performance and finds that it has become a chasm, increasing from 8% in 2001 to 31% in 2012 and 40% in 2014. Without action this gap will grow to nearly 50% by 2020. Mercedes cars have the biggest average gap between test and real-world performance, with real-world fuel consumption exceeding test results by nearly half. None of the improvement in emissions measured in tests of Opel/Vauxhall cars since 2008 has delivered improvement on the road, and their real-world fuel economy is actually getting worse. Just a fifth of the apparent improvement in emissions from the launch of the Mark 7 VW Golf (Europe’s best-selling car) have been achieved on the road. This report shows current systems for vehicle testing of fuel economy and CO2 emissions don’t work and the proposed introduction of the new WLTP test seems likely to deliver limited and only temporary improvements. Systematic changes to the way cars are tested, regulated and taxed are needed to ensure cars are decarbonised on the road and not just in laboratories. The technologies to reduce emissions are available – what is missing is a robust policy framework to ensure these are delivered.