“There are 25 different pieces of legislation in EU member states. Whether the industry could pass the penalties to the consumer I very much doubt,” he said.

Steffen suggested that no single technical solution had been agreed on by carmakers and the variety of CO2-related legislation made it difficult to plan ahead.

He suggested that consumers were increasingly focused on vehicle tax and implied that if list prices rose they would consider this a form of taxation.

Meanwhile, Mercedes sales director Simon Orfield expects to see some sales growth potential from the stricter London congestion charge as all the standard Smart models will be exempt as they emit less than 120g/km.

“We're hoping to get a boost,” he said.