The Man from MI.5 was the seventeenth episode of the first series of Thunderbirds. It was of special note to the Doctor Who universe because of the licensed appearance by the Daleks in the form of a report from the Solturian News Agency, which made it the first ever televised crossover between Doctor Who and another franchise.

Within the context of the ongoing storyline in TV Century 21, The Man From MI.5 was also significant for revealing that other security organisations in addition to the Universal Secret Service, such as the British Secret Service, were keeping updates of the Daleks' progression in space conquest in preparation for their impending invasion of Earth.