Near the end, Sellars gets into taxi KGN 624 and, seconds later, gets out of taxi KGN 686.
When Nicholas Conway arrives at Goring's Depository, late at night, it's dark outside. However, when he is chased onto the roof and flees down the fire escape, it's broad daylight. Once he reaches the ground and goes back to the car that Jean is driving, it's dark again.
After a phone call from Nicholas, Jean leaves her home to go and meet him. She gets in a taxi and it's night, but when she gets out it's light.
At about 22 mins in - Sellars jumps into a taxi and says, "Follow that Hillman," She was in KGY 520. Twenty seconds later it is still KGY 520, but twelve seconds after that, it is KGU 933.
Conway's car is a Hillman Minx. Like most Rootes Group vehicles in the 1950s, it has a white steering wheel. However, in studio shots of Conway 'driving' the car with a back projection road scene, the steering wheel is black.