The amount and color of Ambrose's beer between shots in the scene before the final race changes when Rosalind is hung over. Also, Rosalind's hangover tablets disappear from the table in the same scene.
As the cars race through London towards the end of the film, a group of cyclists following More's car appear and disappear as the camera position changes.
En route to Westminster Bridge, the McKims pass the same blue police box and red telephone box at different points in the race.
Wendy's Party invitation at beginning of the film dated September, however the London to Brighton has always been November.
When Kenneth More gets behind the slow lady driver going by the road works one shot looking back at Kenneth shows no road works.
Towards the end of the movie, having pulled away from the traffic policeman controlling the road junction, Genevieve's rear offside mudguard is flapping wildly. In the next 'in car' scene the mudguard is firmly fixed in place. Not long afterwards the mudguard falls off.
A close-up of Alan and Wendy near the end of the film reverses the shot. There is no apparent reason for this.
When Alan is cleaning his teeth in the steamy bathroom the window he hits to open is pre-cracked and breaks where the lines are visible.
As Kenneth More approaches the bridge his car wheels get stuck in tram lines forcing him to turn right instead of left but the next shot shows the car out of the tracks.
At the end, when Genevieve's brake comes off, the car rolls onto Westminster bridge. The design of that bridge means the car rolled uphill on its own.
At the start of the rally, the cameraman's shadow is visible on the ground and on the car as McKim backs Genevieve into the car park and does the interview.
Kenneth More character at the beginning of the film refers to "vintage cars" without pointing out that the cars in Brighton Run are Veteran not Vintage. No veteran car enthusiast would allow such an error.