I can see the Britannia hangar being built through the window.
Yes, indeed, but it was my recollection that their were offices at that end of the building, occupied by Autair; obviously added later.
Your outside pic must have been taken shortly after the building was complete as you can make out the signal square immediately in front of it. That was soon re-positioned on the other side of the taxiway.
DH87B Hornet Moth in the distance which I would put money on being G-ADKL.