Continuity mistake: In the intro, Dominic Green greets the client from Saint Marie. A few people are passing by the car when he opens the door, but when he closes them those people vanished in thin air. (00:01:55)
Character mistake: In the first scene in the office of the dead banker, Jack is not wearing any gloves and touches the cufflink box freely without any precaution. (00:04:40)
Continuity mistake: The detectives are discussing the presence of the cufflink. Humphrey asks if "He's taken his own life in remorse", and the camera cuts to the deceased. Notice an iPhone on the desk by him. A moment later, the phone rings and Humphrey has to search the victim's pockets to come up with the phone. (00:04:55)
Continuity mistake: Jack and Humphrey are following the taxi in Jack's grey car, the registration number is DG60 SGY when they start following the taxi and LN63 FEJ when they park in front of it. (00:14:50 - 00:16:25)
Character mistake: The first term served by Dwayne's father is typo'd as 4 RS instead of YRS. (00:15:25)
Continuity mistake: Up to the point when Martin West says he took the gun to 'impress the lads', Florence has her hair to the right of her face going in front of the shoulder. New shot, and there's much of it combed back, and it keeps going back and forth until it's again all in the front in Florence's next close-up. (00:26:15)
Revealing mistake: Humphrey and the team receive the decisive last clue from Saint Marie; on the Scotland Yard PC, in the inbox there are tons of emails marked as 'today' that come from places like the Guadeloupe lab and instead days old. (00:34:35)
Continuity mistake: At the pub towards the end of the episode, Jack brings a glass of rum to Dwayne. He hands it to him with his left, but you can see in the shot when he begins to get seated that it's the right arm that he has extended. (00:48:10)
Continuity mistake: When Martha says "Yes" to Humphrey, the waiter in the background has his hands free. She kisses him in the next shot, and in order to clap with the others the waiter has to put down two wine glasses he was holding. (00:49:45)
Plot hole: The big locked room mystery is such only because the detectives build it up as one; they don't make any remark about the fact that the door can be locked from inside without the need of a key, they don't check the door frame or the lock (which would have revealed that it was bashed open while unlocked) and they do not even consider for a moment the idea that someone could have made a copy of the keys, which is the first thing anyone would have assumed. Not just that; nobody on the floor who has been working at the bank for years says anything about some cleaning lady they haven't ever seen before and that happens to be the first respondant to the murder.
Answer: There's probably no particular reason. Sets and props on long-running TV shows often change as needed and for various reasons throughout a series run.
raywest ★