This means that arriving passengers can mix with departing passengers, which technically goes against UK Border Agency policy. The UKBA has apparently told EDI it needs to move towards a common departure lounge, to rectify this anomaly. However, as EDI is currently being sold off, by order of the Competition Commission, it remains to be seen what the new owners will come up with.
Domestic arrivals have nothing to do with the UK Border agency and have been pre-screened to DfT standards at another UK airport, hence there's no issue. The issue would be EDI allowing international arrivals access into the lounge before UK Border clearance or rescreening which given the lack of Flight Connections centre, I don't believe they are capable of?
Incidentally, anyone know why Glasgow is different? They won't allow people back into the departure lounge so if you nip down the domestic pier(s) and your flight is delayed you can't nip back to the shops. I did once ask and the guy made an answer up to keep me happy....we both knew he was lying (!)
There is strict segregation of arriving international passengers so seems to me a little odd. I just like to understand why things are the way they are!
Common use departure lounges are in use at LHR T5 and T1 as well as LGW North and South where arriving international passengers are rescreened prior to access with domestic passengers being photographed (biometrics at LGW) to ensure no one who shouldn't arrives on a connecting flight and connects in the UK avoiding the UK Border. Since neither GLA or EDI have that sort of Flight Connections set up, it's simpler.