The IT Crowd finale is a fitting tribute to a great comedy

It is often said that all political careers end in failure. Even if they don't lose an election – or are forced out by term limits – most leaders carry on beyond the peak of their popularity, gambling that their reputation and legacy might improve. And this rule also generally applies in television: the majority of shows are cancelled because their ratings fall, often following a period in which the network has kept the franchise going because known quantities are always less of a risk in a schedule than unknown ones.

Either side of this weekend, though, there are two rare examples of programmes choosing their own moment to go. The final episode of Breaking Bad (Netflix, from Monday) is driven by artistic logic – not least the fact that the central character was declared terminally ill five seasons back – rather than fall in demand. And, on Friday, The IT Crowd (9pm, Channel 4) achieves the unlikely feat for a British sitcom of leaving the screen because two of the main actors have such prospering movie careers, leading to a commissioned fifth series being willingly fore-shortened to a one-off farewell special.

Chris O'Dowd and Richard Ayoade were little-known actors in 2006 when they were cast as Roy and Moss, the emotionally stunted computer-support staff in the basement of a vague corporation, in Graham Linehan's comedy. Now, O'Dowd is a cinematic leading man (Bridesmaids, The Sapphires), while Ayoade has directed one well-received movie, Submarine, and is working on another, The Double. Showcasing in The IT Crowd has also left Katherine Parkinson – who plays the boys' self-delusional boss, Jen – in high demand on stage (Season's Greetings at the National) and screen: she is currently filming the BBC conspiracy thriller The Honourable Lady.

These happy circumstances mean that the final episode of The IT Crowd is genuinely a lap of honour, rather than, as often with a TV last chance to see, a stumble of shame. Even so, the challenge for a finishing script is to leave fans satisfied and with some moments that repay the attention of long-term viewers. The closing storylines of Breaking Bad, for example, have deliberately caught and tied some threads left hanging very early on.

Most of us would also hope that Breaking Bad will end – as it began – darkly and startlingly, as a bad-taste tragedy demands. Equally, The IT Crowd needs to leave us laughing and with some grace-notes playing off earlier moments, and Linehan handsomely delivers this. The writer has recently been working for the stage (adapting The Ladykillers for director Sean Foley) and this experience may have helped him to execute this final episode because it is a rule of theatre that the mood of a departing audience will significantly be affected by the ending of the play and a satisfying curtain line.

Channel 4 has, reasonably, asked that previews do not disclose the edition's twist, but it is safe to say that the final words spoken are precisely the ones that most viewers would have voted for and that the very last moment is a neat theatrical trick, which, consciously or not, echoes one of Harold Pinter's smartest tricks for bringing a scene to a close.

Before that, Linehan has crafted a sharp farce that turns on contemporary trends (viral videos, Twitter), cleverly incorporates two of the host network's other hit franchises (Channel 4 News and The Secret Millionaire) and, during the final scene, picks up a plot point established during the pilot episode, seven years ago.

The presence of a studio audience increases the feel of the final performance of a cult theatre show and Linehan democratically gives O'Dowd, Ayoade and Parkinson a big solo moment each, a sort of bow to the viewers. The show is left open-ended enough the characters to be revisited one day – if the actors' and the writer's more lucrative employers lose interest in them – but this valedictory special is a masterclass in how a hit sitcom should have the last laugh.