Phileas,
I thought of that... As we may now be into assisted-guessing mode, I'm not sure that Biggin accounts for the backdrop - terrain higher than the airfield but pretty long wavelength stuff...
...and what's that structure? Is it a car park under construction, or a building part-made? It sits comfortably with your little civvie airport theory...
I can't get a sun angle as it's the height of summer, nor are the registrations clear enough to work through the local indexes...
Perhaps we might be told whether it's north or south of a line east-west through Pole Hill?