London, the City, from above. Shiny, thrusty buildings made of steel and glass – the Gherkin, the Cheesegrater etc. Inside one, a man in a sharp suit checks his reflection and strides on purposefully to a meeting, where another man is spouting impressive figures, a pitch perhaps …

What is going on? I was after bumbly blokes, bucolic charm, gentle wit, the occasional unearthing of, if not treasures, then scraps from the past – not the frigging Apprentice.

Wait though, it is a pitch, for a new solar farm. The pitcher unscrolls an aerial photograph of the site, Church Farm, near the town of Danebury. Now, when we go closer in, we can hear birdsong and see two figures, less sharply dressed, less purposeful, ambling, shambling, with metal detectors … They are Lance and Andy and it is Detectorists (BBC4), thank God.

They don’t know it yet, but their patch will soon be covered in solar panels (which may or may not put an end to the birdsong by frying the singers; there is some debate about it later in the scout hut where the Danebury Metal Detecting Club meet).

Anyway, for now Andy (Mackenzie Crook) and Lance (Toby Jones) have treasure – or scraps – from the past to look for, as well as their unsatisfactory lives to run away from. Andy is back from Botswana with Becky and their son, living at Becky’s mum’s; it’s not great. Nor is his job.

Lance has a girlfriend, yay! She’s lovely, but she lives on a barge, boo! Because he gets seasick, and canalsick. And his daughter has moved back in with him, which is great, he tells Andy, meaning it isn’t. She’s messing things up, upsetting the neighbours, cutting the cheese wrong … but he doesn’t want her to go. It’s not easy being an unassertive middle-aged man, set in your ways.

Taking a break under a big, old oak, Andy and Lance have an imaginary dinner party. Stephen Fry and Jesus aren’t invited because they always get invited to imaginary dinner parties. The Dalai Lama neither; he’d probably be a bit moody. Andy might invite Kurt Cobain. “Oh yeah, he’d be a good laugh, he was known for his sparkling dinner party conversation,” says Lance, so deadpan you hardly notice he’s being very funny.

Would there be heroin at this dinner party, asks Andy. The drug talk reminds Lance that one of the friends his daughter has brought home has been smoking “a bit of the old …” and he does a two-descending-notes whistle, accompanied by a smoking gesture.

“Go on, say it,” says Andy.

“What?”

“Wacky baccy.”

“I wasn’t going to say wacky baccy.” Yes, you were, Lance, it’s exactly the sort of thing you would say. Andy knows it, Crook who wrote it knows it, everyone watching knows it.

That’s the thing with Detectorists: you might not be literally rolling on the floor laughing, but it’s so beautifully written and performed – sparse, droll, understated and believable.

Crook avoids falling into the easy traps. Like the mother-in-law stuff – it would have been obvious to make her (Diana Rigg!) a monster, and Andy’s life there a living hell; it’s not, though. They actually get along OK, it’s just not ideal. And the smutty innuendo in the club: it’s not Terry’s talk of moister conditions leading to deeper penetration that’s so funny (yeah, OK, it is a bit), but the infectious reaction of the assembled members, adults reduced to giggling schoolkids.

Andy and Lance’s finds are typically and appropriately underwhelming. A retaining plate from the back of a mid-20th-century socket mount. Then later – and undeniably better – a whistle; a falconry whistle, Lance reckons.

Andy blows it … he obviously hasn’t read the MR James ghost story Oh, Whistle, and I’ll Come To You, My Lad. And it does summon up the past: a girl, a pagan burial ritual, coins, magpies and perhaps the prospect of bigger finds before the solar panels come. That’s another lovely thing about Detectorists: it’s not just a subtle, tender comedy about friendship and middle age and men, their unsatisfactory lives and their weird hobby; it makes a connection with the land and with the past and scraps of lives long forgotten.

Whether or not the solar farm kills the birds, it will almost certainly put an end to Detectorists. Crook has said this third series will be the last. Pity, but then maybe it too can be rediscovered at some point down the line. Future folk can speculate on what it is, be puzzled, perhaps, certainly be charmed.