House Number One and House Number Two.
I'm tempted to go on a photography expedition next time I'm in London, although there are a lot of embassies in the area, so that may get me into trouble. The other problem, of course, is that estate agents seem not to value photographs of entrance halls and staircases, which are of course essential to so many plots. Fortunately, one of my other reference sources has a few I can extrapolate from: House Number One, House Number Two and House Number Two again.
Also, ages ago I found a link to a YSL dress, the copy of which Linda ends up wearing a couple of times in Searching for Julia. Today, I completely forgot where I'd seen it, but having tracked it down, here it is for reference.