The overall draft target for 2020 – of 95 grams of CO2 per km (g/km) for cars and 147 g/km for vans – is expected to remain unchanged.

But sources indicate that the super-credit threshold for cars will be lowered to 35g/km, with a "multiplier factor" of 1.3, and a cap of 20,000 vehicles per manufacturer.

At present, only electric cars such as the Vauxhall Ampera, with its combined tail pipe emission of 27g/km, would qualify for the super-credit scheme. But critics argue that when full lifecycle emissions are counted, even the best performing electric vehicles top around 60g/km.