The software at the centre of Volkswagen’s emissions scandal in the US was built into its cars in Europe as well, though it is not yet clear if it helped cheat tests as it did in the US.

It just didn’t add up. The Volkswagens were spewing harmful exhaust when testers drove them on the road. In the lab, they were fine. Discrepancies in the European tests on the diesel models of the VW Passat, the VW Jetta and the BMW X5 last year gave Peter Mock an idea.