Germany’s premium car manufacturers are allegedly under investigation for collusion over the technology implemented in their vehicles - including emissons-filtering AdBlue.

An article published in German magazine Der Spiegel alleged that Audi, BMW, Daimler Porsche and Volkswagen were part of a cartel which discussed what technology would be offered to customers over a 20 year period – including emissions-filtering AdBlue.

Der Spiegel claimed that the companies are now under investigation by both the German anti-trust office and the European Commission over the allegations.

Share prices in the carmakers fell sharply in the wake of the claims, published on Friday. Volkswagen’s share value dropped as much as 4.9pc; BMW 3.4pc; and Daimler 3.2pc, the Telegraph reported.

Der Spiegel alleged that a cartel arrangement had been uncovered by authorities during a raid on Volkswagen’s offices to investigate suspicions of a separate steel cartel.

Among the items said to be subject of the alleged collusion was the speed at which convertible roofs would operate and the size of AdBlue tanks fitted to vehicles.

Der Spiegel claimed that the group had settled in an AdBlue tank of just eight litres – having tested tanks as large as 35 litres – in light of discussions.

BMW said in a statement issued via its media website that its AdBlue systems were clearly differentiated from other systems and required “a very low AdBlue consumption”.

Commenting on its discussions with other manufacturers, it stated: “From a BMW Group perspective, the objective of discussions with other manufacturers concerning AdBlue tanks was the installation of the required tanking infrastructure in Europe.”

A spokesman for Mercedes-Benz said: “We do not comment on speculation”, with Volkswagen Group also declining the opportunity to comment on “speculation”, stating: "We do not comment on the speculations and misgivings of the Spiegel report.”

The alleged investigations into Germany’s premium car makers, and its suggested link to emissions-limiting technology comes at a tough time for their diesel product lines, Mercedes-Benz’s decision to complete upgrades to hundreds of thousands of UK-owned diesel vehicles having prompted a push to prevent the “death of diesel”.

BMW and Audi have both agreed to retrofit more than 50% of its “Euro 5” diesel-engine cars with software that will reduce their emissions in an agreement brokered with the Bavarian state government as Mercedes embarks on its £195 million “service action”.

  • Has your car dealership experienced a slump in sales or enquiries for diesel cars in recent months? Share your views in AM's latest survey here: