Ms Harris said she wasted a day when she should have been at an important rehearsal after she was twice given misleading information by railway staff, which led her to board the wrong train and then wait for another one that did not exist.
"When I complained, the guard told me never rely on the train service to get you to an airport," said Ms Harris, head of education and training at London's Royal National Theatre. "I asked him if he was being sarcastic - but he said that he was just being realistic."
Ms Harris missed the best part of a rehearsal for her show at the Edinburgh fringe festival after she was forced to change her plane ticket for one departing the following day.
Ms Harris had followed rail information advice and caught a train to Luton airport from London Bridge station.
"I watched the board and got on the train indicated. After it left Waterloo, I realised I was on the wrong train."
Ms Harris caught a train back to London Bridge. There, a guard advised her to take the 7.45pm to Bedford via Luton.
"A train arrived at 7.46pm. The board said it was the Bedford train - but at the very last minute, the board changed to indicate that the train was bound for Charing Cross."
Ms Harris then realised she would miss the plane and had to change her ticket booking - at an extra cost of pounds 50.
She said: "Not wanting to trust the rail system the next day, I drove to Luton and parked my car."
Ms Harris has written to Thameslink asking for a full refund and compensation for the additional cost incurred. "This does not include stress, wear and tear and the fact that valuable time was wasted."
Thameslink has since told Ms Harris that London Bridge station was not its responsibility and that her complaint had been passed on to Connex.
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