The US authorities have begun a legal action against Volkswagen over the scandal that saw millions of diesel vehicles fitted with software that made them seem better for the environment than they actually were.

The US Justice Department filed the suit in Michigan, alleging the car-maker violated the Clean Air Act by installing illegal devices to impair emission control systems.

It is thought to have affected 600,000 vehicles in America, and 11 million worldwide.

VW has admitted fitting the devices and has put aside billions of euro to deal with the fallout.