Lawyers battling Volkswagen Group have shifted their sights towards Bosch, alleging that the supplier was an active participant in the "decade-long illegal enterprise to defraud US consumers.”

The allegation was made as the legal representative of hundreds of Volkswagen owners across the Atlantic submitted a 742-page brief in San Francisco federal court this week, The Wall Street Journal reported.

Bosch was not a party to the recent $15bn settlement on behalf of U.S. Volkswagen customers and still faces civil litigation.

The Wall Street Journal said that Bosch had supplied the engine control unit, which was then programmed by Volkswagen to recognize when its diesel vehicles were undergoing emissions tests.

The US lawsuit claims it was “inconceivable” that Bosch did not know that the software it was responsible for defining, developing, testing, maintaining and delivering contained an illegal defeat device, however, as it did not allow manufacturers to make changes without its consent.

A Bosch spokesman told the Wall Street Journal that the company was “cooperating with the investigations in various jurisdictions, and is defending its interests in the litigation”.