The false CO2 levels have been found as a result of ongoing internal testing following the recent NOx scandal. In its statement, the group said the tests had shown fuel consumption and CO2 emissions figures had been set too low during the certification process. Although the majority of affected engines are diesels, petrols are also included, it added.

The carmaker is now opening a dialogue with type approval agencies, and has estimated the economic fallout to be around €2bn (£1.4bn).

Recently appointed CEO, Matthias Müller said: “From the very start I have pushed hard for the relentless and comprehensive clarification of events. We will stop at nothing and nobody. This is a painful process, but it is our only alternative. For us, the only thing that counts is the truth. That is the basis for the fundamental realignment that Volkswagen needs."

The announcement follows less than 24 hours after the United States EPA issued a second Notice of Violation of the Clean Air Act, alleging that the Group's 3.0-litre diesels used "defeat devices" to cheat NOx tests, in addition to the 1.6 and 2.0-litre engines revealed in September.

Volkswagen said the safety of the vehicles is in no way compromised, and has yet to release details of how large these irregularities are.