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SHT2x LHR-MAN
SHT3x MAN-LHR
SHT4x LHR-BFS [DEFUNCT]
SHT5x BFS-LHR [DEFUNCT]
SHT6x LHR-GLA
SHT7x GLA-LHR
SHT8x LHR-EDI
SHT9x EDI-LHR
They start with the first departure (LHR-MAN) the 0645 so that's 2A then the next flight is the 0700 to EDI so that's 8B etc.
In addition on the domestic sectors the following are used:
BAW12x LHR-NCL
BAW13x NCL-LHR
BAW15x The defunct PLH-NQY-LHR-PLH Brymon round-trip
BAW16x LHR-JER [DEFUNCT]
BAW17x JER-LHR [DEFUNCT]
BAW18x LHR-ABZ
BAW19x ABZ-LHR
Any additional flights non-schedule usually adopt a BAW9xxx flight #/callsign.
Oh, and 'Bealine' is still used for towing BA a/c at LHR for nostalgia's sake 'Bealine Whisky Bravo' etc
I'm off to get out more.