Outnumbered, Series Four, BBC One

From the long shot of the suburban London semis onwards, I couldn’t help but think of the 1960s BBC sitcom Not in Front of the Children which similarly focused on a middle-class couple with three children. There’s no laughter track on Outnumbered but there’s also no escaping the fact that - apart from a colourful new range of insults the kids casually fire at each other (“numb-chuck”, “toss-piece”) - this could easily be one of Wendy Craig’s naughty but nice TV families, bickering over breakfast and complaining about the burnt fish fingers. Oh and look, there’s John Sessions playing the quirky buffoon of a vicar.

So given its conservative-with-a-small-c veneer, how does Andy Hamilton and Guy Jenkins’s Outnumbered manage to stay relevant, watchable and – most importantly – funny, even as it begins its fourth series? Partly because every cosy Britcom cliché is counterbalanced by some sharply current observational comedy (the running joke about texting etiquette, for example) and the ceaseless pleasure of listening to the fantastical interpretations and dissections of the adult world dished up by the two youngest Brockmans (Ben and Karen played by - or rather fully inhabited by - Daniel Roche and Ramona Marquez).

How could you not be both charmed and horrified by Karen’s idea for catching thieves which involved “really small” policemen dressing as children and bubonic-plaque-infected mobile phones with built-in tracking devices? Yes, we all now know a lot of their dialogue is improvised, but it’s also expertly folded into the main storyline like whisked egg whites into a perfect soufflé. We also get the Big Questions dealt with head on. Well, sort of head on. It was Death this week with a side order of Homosexuality. It’s Uncle Bob’s funeral, but shortly before Uncle Bob died he confessed to his wife (in Sainsbury's, for added comic value) that he’d been in a gay relationship for the past 14 years. So Ben gets told off for using the expression “that’s so gay” but Pete’s casually contemptuous mother (a nicely understated performance by Rosalind Ayres) doesn’t get told off for saying, “I’m perfectly at home with gaiety,” although it does tell us all we need to know about the other planet she lives on.

However, what’s most pleasing about Outnumbered is the sleight-of-hand way the excellent cast slips in the one-liners as part of everyday conversation, and just how many of those one-liners there are. At one point Pete’s mum explains to Pete why he has to give the eulogy at Uncle Bob’s funeral, and within a minute she’s outlined half a dozen characters, characters that a lesser sitcom – one painted with broader, cruder strokes – might have built a whole episode around. There was parasailing Uncle Vic with his new hip, Tom who’d be too drunk by midday (the unspoken part being that he’s always drunk by midday) to give the eulogy, and last but not least, someone called Rufus: “His Tourette’s is getting worse. His wedding was embarrassing enough: you’d think he could get through ‘I do’.” A stand-up comic might have made a real meal out of that gag. Yet there it was; a casual aside some viewers might not even catch until the third viewing on DVD.

But the bottom line for this non-parent critic is that Outnumbered amusingly brings home the fact that parents spend a large chunk of their lives shouting the word “no” until it seems to be the only one they ever use. And when they aren’t talking to their children, they’re talking about their children until they all but disappear themselves. Hugh Dennis and Claire Skinner convey this fading-to-grey air of semi-defeated parents perfectly so that viewers either relate to them or thank the gods they are not them, as they somehow find the patience to say the right thing in just the right way to their unnervingly bright yet terminally stupid offspring. Outnumbered? As far as I’ve witnessed it, one child is enough to outnumber its parents.

• Watch Outnumbered on BBC iPlayer
• Find Outnumbered on Amazon