The LHR bound flights normally alternate between Gates 9 and 10, in my experience.

On some evenings the last flight into EDI (BA1464) if parked at Gate 10 will go out as BA1435 (the first flight of the day to LHR) from Gate 10 but on other days it will go out as the second flight (BA1433) with the penultimate flight the previous evening operating the next morning's BA1435. Does that make any sense at all?

It used to be simpler in the old days when one shuttle would push back minutes after the next flight arrived at the adjacent gate.