It strikes me that a significant reason this movie still connects with audiences today lies in how unusual it was at the time—the killing of a police officer then was uncommon, and such an act would immediately draw together both law enforcement and those involved in criminal activity against whoever committed it. This contributes to a believable atmosphere where Dirk Bogarde is excellent portraying a small-time crook who finds himself swept up in circumstances that rapidly escalate. Peggy Evans also delivers a strong performance as the girlfriend experiencing extreme distress. Basil Dearden maintains a feeling of suspense throughout, keeping viewers engaged as the situation intensifies and leading to a compelling ending for this straightforward story.

Source on TMDB