* EarWorm: "It's all right, it's okay"
* HeyItsThatGuy: [[Creator/SharonSmall Barbara]] [[Series/InspectorLynley Havers]] appears in "Queen and Country". Susan Jameson appears as a rich and attractive girl in ''UFO''.
* ItWillNeverCatchOn: TV critic AA Gill has been widely mocked for claiming the show would sink without trace when it first debuted; of course it has not only been going for more than a decade with very high viewing figures, but is also one of the most popular British export programmes.
* MagnificentBastard: MI5 agent Stephen Fisher (played by Tim [=McInnerny=]) in Series 9.
* PlayingAgainstType: Several examples over the years.
** Tim [=McInnerny=], known for playing foppish or pathetic characters on ''Series/{{Blackadder}}'' and an inept villain on ''Series/DoctorWho'', played the sinister MagnificentBastard MI5 agent Stephen Fisher in Series 9.
** [[spoiler:Richard Briers]], known for playing the pleasant [[spoiler:Tom Good in ''Series/TheGoodLife'']], played a villain in "Old Dogs".
* SuspiciouslySimilarSubstitute: Averted with Steve replacing Jack, as they are very different characters. Less averted for Dan replacing Brian, as they are both TheSpock and have family issues (though different ones) and for Sasha replacing Sandra.