Though made in 1957, the film takes place in 1952, but in the opening shots of Sir Wilfrid's car on the streets of London (and in the rear-projection shots in the car's interior), several post-1952 cars can be seen in the background.
Both Sir Wilfred and Mr. Myers introduce evidence directly to the court themselves, which is against courtroom procedure. Sir Wilfred, for example, trumps Inspector Hearne's testimony by directly revealing Leonard Vole's blood type, instead of properly calling a witness with personal or professional knowledge of it.
When Vole and Wilfrid first meet in his office, he refuses to take the case and puts his wig in its container, closes it, and the lid is noticeably 6 inches from totally closed. The next time we see the container it is completely closed.
As Sir Wilfred is cross-examining the Chief Inspector, his monocle chain is over his right collar tab, but after a shot from behind the chain is running under the tab so that when he raises the monocle it lifts the tab up to his chin.
Early in the courtroom scenes witnesses are seated in the hallway outside the courtroom door on a bench. This has a backdrop painted to look like a longer hallway. At the end of the trial when the courtroom is emptied the hallway is shown as being narrower with no bench.
(at around 9 mins), inside his chamber, Sir Wilfrid lights his cigar and Leonard Vole locks the door to make sure that Miss Plimsoll can't enter the room and catch him smoking. But at 14.56 minutes, Sir Wilfrid leaves his chamber without first unlocking the door.
Christine has shaved eyebrows and higher and narrow ones drawn on when she is on the witness stand negating Leonard's alibi. When she is recalled to be exposed for writing letters to Max, she has natural eyebrows, same as the mysterious woman at the bar with the scar.
When Sir Wilfred gives the "monocle test" to Vole, the sun is behind him. The monocle cannot reflect the sunlight from behind. Correctly, when he gives the monocle test to Christine, he is facing the sunny window. She closes the shade to block the sunlight reflecting off the monocle.
The witness Janet McKenzie testified that October the 14 was a Friday. The film is set in 1952; if the year of the murder was 1952, October 14 was a Tuesday or if 1951, October the 14 was a Sunday. The last year October 14 was on a Friday before 1952 was 1949.
(at around 9 mins) Inside his chamber, Sir Wilfrid lights his cigar and Leonard Vole locks the door to make sure that Miss Plimsoll can't enter the room and catch him smoking. Later, (at around 15 mins) Wilfrid leaves his chamber without first unlocking the door. Actually, Vole does not lock the door, but puts the keyhole cover in place to stop Plimsoll spying through the keyhole.
In the first courtroom scene, the clerk twice states that the murder of Emily Jane French occurred in "the county of London". The County of London was known to both Sherlock Holmes and Horace Rumpole. It was run by the London County Council from 1889-1965, was comprised of over two dozen boroughs (Hampstead to Greenwich to Chelsea), and much to Leonard Vole's chagrin, was home to the Central Criminal Courts, the Old Bailey. In 1965, the County of London became the larger, Greater London, which it still is. Administered by the Greater London Council from 1965-86, it has been run since 2000 by the Greater London Authority, headed by a directly-elected mayor and assembly. For reasons of tradition and vested interest, the old City of London, now a square mile of banks, brokerage houses and the Tower, remains a separate entity.
When the photographer takes the pictures of Leonard Vole in the prison, he takes one from the front view and one from Voles right side. Later in the courtroom the prosecutor Mr. Myers shows these pictures to Leonard Vole in the witness stand. Now there is one from the front sight and one from his left side. It is hard to believe, that a professional photographer in a murder case would make such a serious mistake to twist the negative mirror inverted. It more looks like a mistake of the prop master.
When Vole, in his cell, starts relating the story of how he and Christine met, the scene dissolves into a flashback while Vole is speaking. But as it begins to dissolve, Vole, still clearly visible, has stopped talking even as his voice-over continues its narration.
The goof item below may give away important plot points.
At the end of the film, Sir Wilfred prepares to take up the defense of Christine for the inevitable trial for the murder of her husband, however, as an eyewitness to the crime it's not likely he would be able to actually do this.