Hello! I don't actually commute myself but know of loads of people who do - I work for BA.
I think the majority of them use ID 90's after they get them, which are Industry Discount tickets at 10% of the normal price plus tax. They are in general accepted by a few airlines inlcuding BA and BMI (domesticly) But there are people who can tell you more.
Also though lots of people buy loco airline tickets far enough in advance that they are dirt cheap. (only thing is they aren't open like an ID 90 so not felxible if you're delayed back into base but if they cost £10 it's no big deal).
Only thing I'd say is I know a lot of commuters who were temps at worldwide LHR and found the commuting easy and affordable but now they are flying mixed duties from Gatwick it is a bit more expensive and they do have to put themselves up at the Ibis on blocks of Shorthaul/Standby.
Don't know what it would be like if only shorthaul, but I think there are plenty who do it, at BA you can bid for trips which makes it easier.
People at BA do commute from all over the world though. Part Time Cabin Crew come in from as far away as Perth and Barbados so it must be "doable". Certainly once you have your Staff Travel it becomes cheaper if you are coming from further away though domesticly I'm not sure there is much difference between an ID 90 and a "hotline" ticket which is about 5 - 15% below commercial. Because of the damn tax!
As I say hopefully an actual commuter will come on - If you live in Manchester though I know there are plenty of people who drive down?