Jemaine Clement lets a frown form above his black-rimmed glasses. The New Zealand-born actor/composer, famed for being one-half of comic-folk duo Flight of the Conchords, has seen his Hollywood stock rise of late, in films such as Men in Black 3, Dinner for Schmucks and now Steven Spielberg’s latest The BFG. But this laid-back Kiwi is having trouble buying into the earnest nature of studio movie-making.

“I’ve often thought on set: ‘I’m not taking this seriously enough.’ Almost every time,” he says. “It makes me anxious. Everyone’s making notes on their scripts and I haven’t made any on mine.” He recalls his time on the 2015 comedy Don Verdean when he met co-star Sam Rockwell for the first time in rehearsal.

“He had so many notes on his script… I can’t read his writing, I don’t know if they were his grocery list, but he had so many. And I tried on that first day of rehearsal, I wrote a note for an idea – and at the end it was the only note. Even though [Sam’s] really funny, he has a very analytical approach.” Every actor is different, I venture. “Yeah – that’s what I tell myself. I’ve got my thing which is not taking it seriously. That’s my thing.”

Clement may be hard-pressed to take things seriously, but that’s all part of the package. He’s at his best in his New Zealand work: the video-game-store geek Jarrod in Taika Waititi’s Eagle vs Shark and an aged vampire in the hysterical mockumentary What We Do in the Shadows, which he co-wrote/produced/directed with Waititi, a former housemate. “We were both living with our very tidy girlfriends,” he nods, proudly.

Clement, who was born in Masterton on the north island in 1974 and raised by his Maori mother and grandmother, met Waititi at university in Wellington (where he still lives with his wife Miranda, and son Sophocles Iraia). Studying film and theatre, he also met his Conchords partner, Bret McKenzie there. This trio – along with two others – formed the comedy troupe So You’re a Man, devising a show about male body image.

“We toured that a little,” says Clement. “It was hugely successful in New Zealand, then we went to Australia and no one would come to see it, because we were from New Zealand.” In its wake, Waititi and Clement became the Humourbeasts, before Clement and McKenzie forged the Conchords.

Smart songs

Singing smartly engineered songs, the Conchords were the classic example of a cult that went commercial, going from live gigs to radio shows to Grammy-winning EPs to the HBO series, which saw Clement and McKenzie’s folk-singer combo trying to make it in America. It ran for two multi-Emmy-nominated seasons – and everyone who touched it has gone on to further great success.

McKenzie won an Oscar for composing the “Man or Muppet” song for 2011’s The Muppets; Conchords co-creator James Bobin, who directed The Muppets and its sequel, most recently worked with Johnny Depp on Alice through the Looking Glass; Waititi, who directed two episodes, is filming Marvel’s Thor: Ragnarok; and then there’s Clement, working with Spielberg and Oscar winner Mark Rylance on The BFG.

That’s the most fun, performing live. We’ve been writing a few new Conchords songs, yeah

The film is an irreverent children’s tale, based on the Roald Dahl classic about an orphaned girl named Sophie who befriends a giant (played by Rylance). Now 42, Clement was eight when the book was first published. “I had a teacher who was a big fan of Roald Dahl and each new book that came out was a big deal.”

In the film, he plays one of the Big Friendly Giant’s less-than-friendly fellow colossi, Fleshlumpeater. Created via motion capture – Clement had to wear a suit with dots on it, which recorded his movements – and conjured by computer, the end result looks little like him. “I recognise things about myself,” he says, “how I hold my hands… But I have to look for it.” He pauses. “It’s hard to tell if I’d recognise myself. I doubt it.”

Spielberg agrees. “People who know Jemaine in real life are not going to believe [he’s] Fleshlumpeater,” says the director, who calls the actor “the sweetest, most retiring [man]”. With his greying beard and pinched expression, he’s not only unlike his character; he’s the most unlikely of movie stars, music icons or – whisper it – sex symbols. Back in 2007, he and McKenzie made it onto Salon.com’s Sexiest Men Alive list.

This month, the duo are back on stage as the Conchords, performing a US tour. “That’s the most fun, performing live,” he says. New material? “We’ve been writing a few new songs, yeah.” He’s a little reluctant to let on more about the Conchords, although there is talk of a movie version that he and McKenzie are chipping away at.

There’s also a TV show he’s co-writing with Waititi and American comedy maestro Judd Apatow – a four-part series of “mini-movies” that will see the same cast play a different set of characters in each episode. On the acting front, he’s been filming the New Jersey-set indie comedy Humor Me, in which he plays a struggling playwright who moves in with his joke-telling father, played by Elliot Gould.

For all his success, you get the impression Clement would rather be chucking ideas around with Waititi and McKenzie. He can still remember hawking What We Do in the Shadows around Hollywood. “We were having meetings with big companies like Sony, and they were saying: ‘Who’s in it?’ We’d say, ‘Our friend Jon, who is so hilarious. He did a play about cricket that he wrote himself.” You can sense the tumbleweed; no wonder Clement doesn’t take the business seriously.

‘The BFG’ (PG) opens next Friday