An update on my situation: booked a flight for next year and went to put in my plus card number and was told it was invalid. Phoned them up: took about five attempts for her to get the number then she put us on hold and never came back. Phoned again; my card had been inactivated but she sorted that out and said it wouldn't happen again....we shall see. Just keep a copy of your original emai with the plus card number and you should be ok on board to get your discount.