You can either appear as yourself, like Lorraine Kelly and Jim Watt did, or play a memorable one-off character, the path chosen by Sylvester McCoy and Robbie Coltrane.

US-based comic Craig Ferguson took the latter option in tonight’s series finale of Still Game, turning up as a seemingly ageless former stuntman who left Craiglang 50 years previously and is now looking to rekindle a former romance with Isa.

The pay-off (the fit OAP routine was just a ruse and he was in fact a chubby bold eunuch) worked quite well, but the journey to the punchline showed some of the glaring problems since the iconic Scottish comedy series returned after a near decade long absence.

Fans, deprived of new material, watched and rewatched the first six series of Still Game in that gap, and, facilitated by binge-watching on Netflix, became experts on the show.

Sadly, it appears that the writers of Still Game, Greg Hemphill and Ford Kiernan, aren’t experts on their own creation, as highlighted by muddled writing and continuity errors in this current series, the show’s eighth.

As Isa pondered whether to ‘go the whole way’ with stuntman Callum, she discussed her difficulty in moving on from husband Harry with Navid and then Winston.

That would have worked had the lovelorn Isa not previously courted Winston, snogged Navid at a New Year’s Eve party, and had an entire episode subplot (in ‘Hot Seat’) dedicated to her attempts to find romance after her estranged husband’s death.

Treading old ground has been a recurring theme in this most recent series - in the fifth episode, a routine about how far abroad the main characters had slept with someone, was a rehash of a segment in the original Still Game live show.

Craig Ferguson hints at his starring role in Still Game '˜spin-off'

Perhaps even more egregiously, the main plot of last week’s episode revolved around a fight in the Craiglang butchershop with Peggy was a note for note retread of the show’s second episode, with only the meat in question changed.

It seems the writers haven’t taken even a cursory glance over their own previous episodes, leaving the last two series’ looking like an entirely new show.

These aren’t minor issues like a pint glass out of place in the Clansman, but glaring errors like the apparent disappearance of Tam’s son, and Methadone Mick going from poetic culture vulture to nasal idiot whenever the plot demanded it.

Still Game’s episodes were often formulaic, but that wasn’t necessarily a bad thing in early years.

Sitcoms like this rely on tried-and-tested tropes (misunderstandings, long-lost reunions, new experiences) and what made Still Game so beloved was not intricate plot lines, but hilarious patter.

Some of the punchlines of these series would have ended up on the editing room floor in previous years, but with the writers seemingly on autopilot, no wisecrack is too bad to miss the cut.

Time has taken its toll on some of the actors too, with a decade spent dabbling in panto leaving some characters, particularly Isa and Boabby the barman, caricatures of their former selves.

While the viewing figures remain strong (as they have been this series) we will likely be seeing Still Game on our screens for years to come.

Even the best sitcoms, however, have to learn when to call it a day.

As incredible as the earlier episodes were, it seems for Still Game, that day has arrived.

In truth, as tonight’s episode showed by failing to raise a chuckle, that day arrived before this series even aired.

Still Game Review: Muddled finale sums up dismal series