Casting of leads like Guy Pearce and Damian Lewis aligns with historical figures without alterations. However, the show introduces a prominent fictional MI5 character, Lily Thomas (Anna Maxwell Martin), explicitly added to diversify the cast and serve as a vehicle for critiquing the 'old boy network,' British class privilege, and patriarchal structures in MI6. Her subplot includes pointed dialogue attacking the elite 'toffs' and features an African husband as a moral counterpoint.

The writer, Alexander Cary, has publicly defended the addition against accusations of political correctness, stating that if it is 'woke,' 'bring it on,' and framing it as correcting unsung female heroes. Conservative reviews highlight this as an ahistorical imposition of modern feminist and classist ideology, with the character functioning as a mouthpiece for contemporary social commentary rather than organic storytelling. These elements influence subplots and thematic framing without becoming the core premise, which remains the male friendship and espionage betrayal. Audience pushback from traditionalist outlets labels it as injecting unnecessary progressive messaging.