When Mrs Brown’s Boys first became a hit on the BBC, there was widespread consensus among the cognoscenti that it was a harbinger of the imminent downfall of western civilisation.

But Brendan O’Carroll has defied the snobs to merrily churn out his no-brow sitcom for 15 years now – and still the world continues to turn. Whether Mrs Brown’s Boys has a future is harder to say – ratings have plummeted from a peak of 13 million to just two million last December, and O’Carroll has said that he would have no complaint were the BBC and RTÉ to call time on the series and the seasonal one-off.

You do have to wonder if his heart is still in it because this latest Xmas one-off (RTÉ One, 9.05pm) is among O’Carroll’s flattest festive forays yet. There are barely any gags, and a typically enthusiastic turn by O’Carroll, playing Finglas Mammy Agnes Brown, cannot paper over the paucity of zingers.

As is the tradition with these Christmas instalments, the plot is mushier than Brussels sprouts that one of your dinner guests has stomped into the carpet. Agnes’s grandson Bono is angry about his parents’ break-up while Mrs Brown’s daughter, Cathy (O’Carroll’s real-life wife, Jennifer Gibney), is eager for the family to speak more honestly about what they do and don’t want for Christmas.

You can see what O’Carroll is getting at here. Christmas is difficult and frustrating, but once you have your family, does anything else matter? But that entirely laudable message is attached to a chuckle-free sitcom that doesn’t even have the energy to be in poor taste. Oh, for a gag about breaking wind or a well-deployed single entendre to interrupt the monotony.

Mrs Brown’s Boys review: It’s surely time for this dreary and unfunny series to fade from our screensOpens in new window ]

There are a few serviceable one-liners – if by serviceable we mean that they would have passed muster in a British workingmen’s club in the 1970s. “I’ve just had a big epiphany,” says Cathy at one point. “I’ll get the plunger,” deadpans Agnes – to reluctant hoots from the studio audience who sound as if they are being held hostage.

Ireland has shared a few iffy exports with the world across the decades – from Ronan Keating’s Fairytale of New York to Paul Mescal’s attempt at sounding like Russell Crowe in Gladiator 2. Mrs Brown’s Boys isn’t quite as off-putting – but even for a retro sitcom, it is clearly past its sell-by date. Taking up the theme of Christmas honesty as expounded in the episode, perhaps Mrs Brown should heed her own advice. It’s time for this creaky comedy to enjoy a well-earned Christmas break.