There's still a lot of old houses in Greater London!
Sparrows seem to have been ousted over the years by large numbers of pigeons, supplemented more recently by massive Seagulls!
As for being airtight, the house next to ours when we lived there, was rented out to a large eastern European family who seemed oblivious to the large family of pigeons living in their roof.
Our daughter sent us a picture of our old house (although I'd already dseen what the new owners had done on Google earth) which has followed the modern fashion by being painted grey (yuk!)
Unless something has been done about the pigeons, it won't stay in pristine condition for long - they enter and leave between the bay and property boundary and the window sill of the bay in particular has heaps of excrement on it and running down the walls. Needless to say, the pigeons don't keep to their own side of the boundary!
You can get a good idea of what it looks like here: