Its an interesting one. BA never did LGW-GCI, in fact LGW-JER was originally British Caledonian. LGW-GCI was British Island Airways using Dart Heralds (whoops showing ones age here!). Certainly in those days the runway would not take a jet of any kind. They became Air UK which these are the forrunners to FlyBe.
Certainly up to about two years ago you could book MAN-EDI on Flybe through ba.com. But no tier points, miles or OnBusiness points