In the series, the idea was made on the concept that MI5 officers have temptations to make money. The written scenes where Salter confesses to Tom was somewhat inspired by Tinker, Tailor, Soldier, Spy. The scene was for the two to act as friends rather than interrogator and suspect.
The concept behind the series centered on the notion that MI5 officers are vulnerable to financial temptation, echoing the themes present in the novel Tinker, Tailor, Soldier, Spy. The scene where Salter confesses to Tom was intended to showcase a moment of camaraderie between the two characters.