Just before attending the armed robbery at QTZ, a watch shows it is 10am. After the chase Regan's phone displays the time as 16:15. Also, the large white Samsung with no signal clearly differs from the black phone he was using in the car when being told to stand down.
In the gun fight outside the private bank, the rear window of the Volvo that Jack Regan is crouching behind keeps reverting back to intact glass between shots, repeatedly shattering in the same place after being fired at.
During the car chase through the caravan park, Carter can be seen leaning out of the passenger side window to shoot at the other car. In the next shot, the window has (very quickly) been rolled back up and Carter is sitting back in the seat.
When the character Francis Allen is told he can leave. He gets up and takes off the jump suit that been provided for him. Because he had been arrested in his underwear. After he completes removing the suit. He walks around the corner of the desk. No one in the room has moved. Except him. But as he rounds that corner his hands are now behind his back and he's handcuffed. There's no explanation for how that came to be.
During an arrest scene one of the characters says to the suspect: "You have the right to remain silent..." This is part of the Miranda used by United States law enforcement and would not be used in the UK. In Britain the caution that must be given at the time of an arrest begins with, "You do not have to say anything but it may harm your defense if you do not mention when questioned something that you later rely on in court..."
Numerous characters including George Carter refer to their police rank as Officer. This is incorrect as no such rank exists in the UK Police. The correct rank is Constable and as such, he is Detective Constable George Carter.
Uk prisons use a Telephone PIN system and a prisoner can only make phone calls to numbers that have been checked and vetted this is to stop prisoners harassing victims and witnesses or talking to anybody involved in the case/crime they are imprisoned for. It takes several days to add a number to a prisoners PIN and even if enough time had passed to do this it is unlikely Jack would be allowed to contact Carter as he attempts to do in the movie.
When George aims to take a shot at the bank robber who is fleeing on the bicycle and then fires at him, a click sounds to indicate he is out of rounds. If the pistol was out of rounds then the slide would be locked in the rear position, which it is not.