//Method to delete the set of car hire details from a set booking of
        //a set customer within the list of customers.
        public void deleteHire(int CustomerID, int BookingRef, String DriverName)
        {
            Booking booking = findBooking(CustomerID, BookingRef);
            HireCar hDel    = this.findHire(CustomerID, BookingRef, DriverName);

            if (hDel != null)
            {
                booking.Hires.Remove(hDel);
            }
        }
        //Method to add a new set of car hire details to a set booking of a set
        //customer within the list of customers.
        public void addHire(int CustomerID, int BookingRef, HireCar hire)
        {
            Booking booking = findBooking(CustomerID, BookingRef);

            booking.Hires.Add(hire);
        }