The neck has been redesigned by Audi to ensure it cannot accommodate petrol nozzles. An internal fuel flap will open only when the larger diesel pump nozzle makes contact with it. The smaller diameter petrol nozzles do not make contact, so the filler flap remains closed and prevents access to the reservoir. It will also prevent any spillage on the forecourt.

This latest advance will be of particular interest to companies running vehicle fleets, but will also reassure for private motorists making the switch from petrol and those who aren’t the car’s sole user.

The newly-equipped cars in the A4, A5 and Q5 family will be joined by further Audi models soon as the system is rolled out gradually.