Continuity mistake: When Gary is on his motorbike going to the agency in London he is riding down a country road with trees and hedges on both sides, but when the camera is looking into the mirrors on the bike there are houses at the side of the road.
Continuity mistake: When Gary is in the restaurant with Julia he writes out the card asking Joe Baker to join them. As soon as Gary picks up his pen the angle changes and the note is written in full.