Germany’s biggest carmakers are being investigated on suspicion of ­operating a secret technology cartel for the past 20 years that led to the dieselgate emissions scandal, it was claimed today.

Daimler, BMW, Volkswagen and the two VW subsidiaries, Porsche and Audi, have been meeting in secret to agree on the technology they will ­offer their customers, according to allegations published in Spiegel magazine.

The collusion was a direct cause of the diesel emissions scandal, which emerged at VW two years ago, after the five carmakers agreed to limit genuine emissions cleaning technology, the magazine alleged.