Continuity mistake: Juliet arrives at Mark's flat and brings banoffee pie with her, wanting to see the wedding video. She slips the video into the VCR and places the open pastry box on top of the TV stand. As she takes her jacket off the pastry box is gone, yet in the next shot of the TV the box is right next to the remote, which then changes position in the last shot when the remote disappears. The TV is in the center of the stand in some shots, but to the left of the stand in other shots. The video cassettes, etc., change/alter their position within these shots as well.
Continuity mistake: After Sarah has called at Harry's office, Harry prepares to open his office door to see her out. The camera cuts back to Sarah for a moment, then back to the camera angle on Harry as she walks to the door. In that short space of time, the sliding cupboard doors have changed their configuration, and the blinds in the upper left of the frame have partially closed.
Trivia: Billy Bob Thornton agreed to appear in the movie without having seen the script. On the day of shooting he told director Richard Curtis that he was scared of Benjamin Disraeli's facial hair, and as such wouldn't be able to do the scene in Ten Downing Street because there was a picture of him on the wall. Curtis told him to keep his back to the picture throughout the scene, which he does, although you'll notice he looks quite nervous.
Natalie: Hello, David. I mean "sir." Shit, I can't believe I've just said that. Oh, and now I've gone and said "shit" - twice. I'm so sorry, sir.
Prime Minister: It's fine, it's fine. You could've said "fuck", and then we'd have been in real trouble.
Natalie: Thank you, sir. I did have an awful premonition that I was going to fuck up on the first day. Oh, piss it!
Harry: Tell me, exactly, how long it is that you've been working here?
Sarah: Two years, seven months, three days and, I suppose, what, two hours?
Harry: And how long have you been in love with Karl, our enigmatic chief designer?
Sarah: Ahm, two years, seven months, three days and, I suppose, an hour and thirty minutes.
Harry: I thought as much.
Sarah: Do you think everybody knows?
Sarah: Do you think Karl knows?
Sarah: Oh that is bad news.
Harry: Well I just thought maybe the time had come to do something about it.
Sarah: Like what?
Harry: Invite him out for a drink and then after about twenty minutes casually drop into the conversation the fact that you'd like to marry him and have lots of sex and babies.
Karen: Tell me, what would you do in my position?
Harry: What position is that?
Karen: Imagine your husband bought a gold necklace and come Christmas gave it to somebody else...
Harry: Oh, Karen...
Karen: Would you wait around to find out if it's just a necklace, or if it's sex and a necklace, or if worst of all it's a necklace and love? Would you stay, knowing life would always be a little bit worse? Or would you cut and run?
Harry: Oh, God. I am so in the wrong. The classic fool.
Karen: Yes, but you've also made a fool out of me, and you've made the life I lead foolish too.