After Bagley has lunch with his wife, she drops him back at the advertising firm's office building, but it is a different building to the one used for the interior scenes, which is the tall red building several hundred yards up the street (visible in the crane shot of their car pulling up), right next to the Lambeth bridge, as we can see from the window view in the scenes in Bagley's and Bristol's offices.
During the anniversary party, the strap on Julia's dress changes shoulders for one scene. When the dress is on the opposite shoulder, it looks a different colour as well.
Julia's nail polish color changes from the closeup of taking the briefcase to the closeup of her opening it.