When Mr. Pershore retrieves the £500 that he had found in Fuller's safe, he and Gently note that the notes are sequential from D671271 to D671371, which would be 101 £5 notes, or £505.
When Bacchus shoulders down a door, the door frame and very modern-looking striker plate remain visibly intact, meaning it wasn't actually locked.
Draper's body had been pulled from the river, but his clothes appeared to be completely dry.
The episode is supposedly set in 1964, but in the Pershore campaign headquarters there is a pinball machine "Creature From the Black Lagoon" which, according to the International Pinball Database, was not manufactured until 1992.
In Geoffrey Pershore's campaign office there is a poster of the Muhammad Ali vs George Foreman fight on the wall. This fight took place on October 30, 1974 which is 10 years after the setting of this episode.
Jimpson threatens to cut Pershore's throat with a broken glass, and Gently asks if he is worth hanging for. This was on election night, 15th October 1964, and under the Homicide Act of 1957 such a killing would not receive a death sentence, Gently would have known this. Also it was well known that if elected Labour would end the death penalty, which they did. The very last UK executions had been in August that year.
You hear the Byrds' 'Turn Turn Turn' song being played; the song was released in 1965.