The Prince does not own or choose to drive around in a Bentley. The car is required for some engagements for security reasons and is owned by the Metropolitan Police. Normally, The Prince and The Duchess are driven around in a Jaguar XJ and a range of new low and zero emissions vehicles.
He also leases diesel vehicles for use when he is in the countryside.
In order to reduce net emissions from car travel, The Prince's Aston Martin runs on bioethanol made from wine wastage and a by-product of cheese-making.