Looking at the Summer 1971 editions of the Birmingham Airport monthly timetable (available from the airport shop for 2.5p!!) it seems the Comet fleet operated a 4 day programme for Lyons Tours between Friday and Tuesday, service GRO and PMI. The aircraft must have positioned in on Friday afternoon / evening, and positioning out on Tuesday morning. I imagine it operated a Tues to Friday series from another airport, can anyone recall which that might have been?
Interestingly said timetable was showing flight number with prefix "LY" which is clearly nonsense since that was and is the IATA code for El-Al. I cannot recall what was shown on the airport departures board, but surely it couldn't have been LY, and I would have though it ought to have been CW. I'd be interested to know whether LY was actually used, and how that could have been. LY was obviously a reference to the tour operator LYons.