Continuity mistake: When Helen arrives home after being sacked (in the version where she doesn't catch Gerry in bed) he calls out to see if it's her. She replies "No, it's your bit of stuff. Wednesday, shag day, remember?" However it's been made clear from Helen's attempted replacement of the booze she took from work on Friday that it's actually a Monday.
Continuity mistake: Just before Helen gets hit by a car, it is pouring with rain, and she and James are soaked, although when she is about to cross the road, the rain has stopped and they are both suddenly dry.
Continuity mistake: In one scene when Helen has short hair, she is talking to Gerry. As the camera cuts between her and Gerry, her fringe alternates from being behind her ear to hanging down her face.
Continuity mistake: When Helen catches her boyfriend in the act, we see very briefly that there is a gap between the bedside cabinet on which the radio cassette player is sitting and the wardrobe. This is more clear when her boyfriend switches off the music. Later when the other Helen comes home and her boyfriend leaps onto the bed to hide the earring we see they are much closer. Granted Helen now has two parallel lives but that can't explain the change.
Factual error: At the beginning, when Helen is running for her train, the station signs clearly say Embankment. However the type of train that she misses/catches is specific to the Waterloo & City Line, which only runs between Bank and Waterloo - it doesn't go anywhere near Embankment!
Continuity mistake: When Gerry spots Helen at the post rowing activities he peers through the window. We can see 3 glasses from his side, one half pint glass partly hidden by the window frame and 2 pint glasses visible through the pane beside the one he is looking through. The shot from inside only shows two pint glasses in different positions.
Continuity mistake: On the train when Helen is speaking with James, her hair goes from being behind her ear to being in front.