Circa 1985 Mrs A to be and I were flying LUT - AGP with Monarch. There was also a Britannia flight doing same route at same time.
Boarded the 757 and was idly watching a (Virgin?) Viscount being started on next stand when it became apparent that CC were having a 'flap'. Repeated trips up and down cabin counting heads, comparing notes and conversing with dispatcher. Eventually there was a request to check tickets etc and a young woman down the back was deboarded and went back through the terminal to board the BY737 further down the apron.