I have rated this very poor because of the problem on exiting. We tried to exit within the permitted time, having pre-booked this. However, on inserting the ticket at the barrier I was informed that £133 was due. I repeated the process with the same result. This was at approx. 2330 on the 24th May. Fortunately my dilemma was seen on CCTV and your officer on duty phoned through and asked about my problem. I told him, plus my name and booking reference and after he had checked these detail he opened the barrierand all was well. Such an error should not happen, particularly late at night when we were stressed after the flight and anxious to get home. The officer himself was very helpful.