The German transport minister has asked Tesla to stop calling its cars' autonomous driving feature 'Autopilot', on the grounds of it being misleading to consumers.

Autopilot is a suite of driver assistance features fitted as an optional extra to the Tesla Model S and Model X.

The system can regulate the car's speed, speeding up, slowing down, starting and stopping to follow surrounding traffic. It can also control the steering wheel to keep the car in its lane, or switch lanes when the indicator is used by the driver. In extreme cases, Autopilot-equipped cars can swerve to avoid collisions with wayward vehicles.

But naming it after an aeroplane's autopilot system is wrong, claims transport minister Alexander Dobrindt, who wrote to Tesla on behalf of Germany's Federal Motor Transport Authority (KBA) to request the name is changed.

Confirming a report in daily newspaper Bild am Sonntag of Dobrindt's actions, a ministry spokesperson told Reuters: "It can be confirmed that a letter to Tesla exists with the request to no longer use the misleading term Autopilot for the driver assistance system of the car."

According to Bild, the request sent to Tesla read: "In order to prevent misunderstanding and incorrect customers' expectations, we demand that the misleading term Autopilot is no longer used in advertising the system."

A Tesla spokesperson defended the use of Autopilot, saying it is a word used in the aerospace industry for many years to describe a system operating alongside a human pilot. "Just as in an airplane, when used properly, Autopilot reduces driver workload and provides an added layer of safety when compared to purely manual driving," the spokesperson said.

The request came soon after the KBA wrote to German Tesla owners, warning tem that their cars could not operate without their constant attention, and that the law states drivers must remain alert and responsible no matter what autonomous systems the car is using.

Tesla is not the only company struggling with the linguistics of autonomy. Mercedes was forced to remove a US advert in July after complaints about it describing driver assistance features as 'Drive Pilot'.