Why did Mackenzie Crook turn down Pirates of the Caribbean to make a BBC4 comedy?

It's a tidy metaphor for his show: a beautiful gem, relatively hidden away on BBC4 but discovered, loved and treasured by a growing army of enthusiasts. Quite rightly it won the Bafta for best sitcom earlier this year.

It's tender, emotionally honest and funny. It presents male friendship and obsession without resorting to the clichés of football and laddish-ness. And it explores the idea that beyond trudging through a field looking for buried treasure, these men are really looking for far more.

Crook as Ragetti in Pirates of the Caribbean

It is a labour of love for Crook, who admits he rejected another turn as pirate Ragetti, the glass-eyed comedy member of Captain Barbossa's crew in the blockbuster franchise Pirates of the Caribbean. "When it comes down to it;' smiles the actor shyly, "it's a choice between doing a character again that I first did 12 years ago – and it's a little part in a big Hollywood movie – or doing my own passion project."

There was, it seems, no choice. Still, it's not as if there isn't plenty of Hollywood stardust in Detectorists. Diana Rigg has a cameo role in this week's episode. And starring alongside Crook is Toby Jones, playing the lovelorn and loyal Lance, best mate to Crook's odd-job man Andy. Crook first approached Jones, who had never really done this kind of comedy before, after meeting him on the set of Muppets Most Wanted, starring Crook's old compadre from The Office, Ricky Gervais. And he couldn't be happier with the casting.

"Toby trained at Lecoq [theatre school] in Paris, where he learnt these incredible clowning skills and this physical comedy, and that comes across... the things he does, the subtle little physical traits... just beautiful to watch. He
decided that he wanted to be from the West Country... he just sort of owned the character. Also, he's a funny guy himself."

In series one, Jones's character was beset by his ghastly ex-wife Maggie, played by Lucy Benjamin. Lance is now moving on (perhaps to internet dating if he takes up Andy's advice) and Maggie won't appear in series two. Lance also won a fortune on the lottery but he doesn't tell anyone – money clearly doesn't matter much in Crook's universe, whether on or off screen.

The new run also sees Andy, now married to his girlfriend Becky (Diana Rigg's daughter Rachael Stirling), as a stay-at-home dad fretting nervously about their baby. He has feeding schedules and strict routines that inevitably get ignored, sending Andy into a nervous tailspin.

When Radio Times meets him, Crook is also fretting, in this instance about his smoking. His wife had just bought him an E-cigarette to help him quit in time for his birthday – he turned 44 last month. He shuffles around uncomfortably in his seat, head bowed, mumbling slightly when he speaks. He seems to dislike fame and being in the spotlight.

"I have five herniated discs in my neck, which flared up when I was in New York a few years ago:' he says, glancing up slightly. "The doctor reckoned it was a ten-year-old injury and asked me if I could remember any incident, and I can't remember any specific thing, but I do wonder whether it's years of wearing a baseball cap and looking at the floor."

How Detectoristy, I suggest. "I know! I don't want to moan about it too much because who wants to hear someone like me whinge, but yes, it's never sat very comfortably with me. But again, it depends on what mood you're in. If you're in a good mood, you don't mind people coming up and saying hello. And people only ever say nice stuff to me. Things like 'Wahey! Where's your stapler?', that kind of thing. Detectorists fans aren't rowdy in the pub."

Crook as Gareth in The Office

He admits longing to melt anonymously into a cosy bar when he goes out, but knows those days are probably over for him now. Although he does present a fairly normal dad to his two children when he does the school run from the north London home he shares with his wife, former advertising executive Lindsay (whom he met in 2000, "before all this madness kicked in"). And he's careful to avoid social media, not least because he's tired of having his personal appearance constantly mocked.

"People do go on about how skinny I am... You couldn't get away with just focusing on a woman's size these days, but it seems to be all right to do that [to a man]. It makes me a bit cross sometimes.

"So when I go out, I am particularly recognisable, I think The only person I hang out with who is more recognisable is Matt Lucas, who is recognisable from 100 yards away. And he gets it constantly... people taking photos or double-taking.

"People project things on to you. Gareth [his character from The Office] was an odd-looking bloke, with the hair... so therefore people will always think of me as a pale, unhealthy, pasty-looking weirdo. And people also hear a West Country accent when I'm talking, when there isn't one. I am from Kent! My accent is Kentish!"

One solace is metal detecting and he has taken up the pastime with enthusiasm.

"While we were filming, I metal-detected on my day off and I found some great stuff just where we were filming in Suffolk. We got permission from a farmer there. I found a silver sixpence, James I in 1610. That was pretty good."

It was, he reckons, worth only about £50, but any man who turns down Hollywood isn't about the cash value. So why has he taken up the hobby – is it to further explore his character?

"I don't know if it's that, or a genuine passion for history and metal detecting – it's very exciting. When I found this silver sixpence, I was the first person to touch that since whoever dropped it back then. It's incredible! It's like time travel – a direct connection with whoever dropped it however many centuries ago. And it's very meditative. It gives me time to think."

Crook grew up in Dartford but he's a country boy at heart. He has bought eight acres of Essex wood-land to take his children. "I grew up in suburbia but I spent all of my time down at the river – it was only a short skip to the countryside – I was on the margins looking longingly out.

"When I wrote the first series I knew metal detecting normally happens in the autumn and winter months when there's no crops in the fields - because you can't go to dig up a field of crops – so they wait. So when I wrote it, I imagined it in a much bleaker, grey world of biting winds and mud, but we shot the pilot in the summer and I just realised that I'd be a fool not to shoot it in the beautiful English countryside in the summer, so that's very much part of it as well."

The BBC want a third series of Detectorists, he adds, which may happen if he gets the right ideas. "To be honest, I've not really had any great periods of time since The Office where I have been out of work or where I have been despondent about what's going to happen next. I think I've always been waiting for it to come crashing down, which is why I was very keen to make this programme and create something for myself. This means... a lot to me." A found treasure indeed.

Detectorists return to BBC4 tonight (Thursday 29th October) at 10pm