I was once on a BA flight to Milan, early morning departure from LHR, early 1982 I think it was, the aircraft was a Trident. There had been some system problem with check-in/boarding pass printing at Heathrow and there was a Munich flight departing at a similar time from an adjacent gate. We were sitting in our seats at the gate while the cabin crew TWICE did a head count and asked every row of Pax if they were travelling to Munich. No answer from anyone, most noticeably the pin-striped banker type in the row in front of me, who kept his head down in his Times. It was only as we were taxying to 10R and the Captain announced "Good morning Ladies and Gentlemen, and welcome to flight BAxxx (568 I think but can't be sure) to Milan, that said banker type exploded "Milan? Milan? I'm going to Munich!!" We pulled over when about 4th in line to depart, so he could be taken off the aircraft. I always wondered if the Munich aircraft pulled over as well.