Jez Butterworth on punching Harvey Weinstein, his unconventional childhood and his new show Britannia

• Sky Atlantic’s Britannia: “Game of Thrones meets the most debauched year you ever had at Glastonbury”
• Meet the cast of Britannia
• Britannia’s warrior women on why it’s a girl power drama

Inside, all falls into place. A Yorkstone entrance and stately staircase; a large black-and-white photograph of Chuck Berry above an empty pram. Upstairs, in the drawing-room an oversized black-and-white lacy lampshade sits on a sofa, a striking photo of Miles Davis is on one wall, a painterly one of David Bowie on another.

His study is a fabulous meeting of Victorian parlour and Biba: huge ferns and rubber plants, old antique carpets, battered leather chairs, a sofa covered in a fabric involving mirrors and layers of embroidery. A set of Wisden’s Cricketers’ Almanack, with their distinctive yellow spines, on the bookshelf. On the mantelpiece are photograph cards of some of his heroes: David Hockney, George Bernard Shaw, Tom Stoppard, TS Eliot, Edith Sitwell, Vanessa Bell, Seamus Heaney, Leonard Cohen.

On a far wall, there are photos of his daughters, Mabel and Grace (11 and eight) from his first marriage to film editor, Gilly Richardson. And one of his late sister, Joanna, who was the oldest of the five siblings – an attractive dark-haired woman, larking around with Butterworth’s brother, Tom, a co-writer on a number of projects, including the current one, Britannia, which is his first major foray into television.

In his shirt and jeans, silver shaggy hair flecked with black and matching bushy beard and tache, the writer reminds me of one of those laid-back, slightly dishevelled West Coast musicians – Lowell George, Dr John or maybe a Doobie Brother. He wouldn’t look out of place in a Laurel Canyon album cover from the 1970s, which he might well take as a compliment.

Britannia is a highly original, trippy take on the Roman invasion of Britain and the theme music is the Scottish psychedelic-folk singer Donovan’s mesmerising 1968 hit single, Hurdy Gurdy Man, about a wandering holy man who comes “singing songs of love”.

“That was from an album we had when we were growing up,” Butterworth explains. “The Best of Donovan was among a quite small record collection that my parents had.” He still has the record in a cupboard in his study. “I listened to that song growing up and loved it and when I was writing Jerusalem. When I had nothing [to go on], at the very beginning, I sat down at a desk and I had that song on a constant loop for about a week. Just the one song.

“I was trying to get to something that’s in that song, which I wanted to put in the play. I think I got some of it. And when it came to writing Britannia – which is along similar lines in lots of ways – nothing else fitted so well. I think it is a spell, that song.”

Spells, magic, anarchy and destruction in Arcadia, gods, spirits, nature, ancient pagan ritual… these are themes that feature in Jerusalem, The Ferryman and now Britannia. All with a great soundtrack. When we talk about the way he creates the atmosphere of his home and workplace, music is integral. “I want to sit down and get my music on, and as it goes dark in this room, and I light candles in here, it doesn’t feel like a room where…” a big chuckle of a laugh, “something boring’s gonna happen, you know!”

Britannia came about through a friend of his, its producer James Richardson. “It sounded like an intriguing idea and for many years I’ve been obsessed by periods of history where one set of gods collides with another set of gods and what comes out of that,” he says.

It’s a ten-part series filmed in the Czech Republic and set in AD 43, after Julius Caesar’s failed attempt to conquer Britain. There are Roman soldiers (the General is played by David Morrissey), Celtic chieftains and warriors (Zoë Wanamaker, Kelly Reilly and Julian Rhind-Tutt) and very creepy Druids in a landscape littered with skulls, reminiscent of Colonel Kurtz gone AWOL in Apocalypse Now – “The horror, the horror”, indeed. The credits weren’t available for the two episodes I saw, so when Butterworth talks about Mackenzie Crook (who was also brilliant in Jerusalem) being the chief Druid, I am flabbergasted, special effects notwithstanding.

“He is terrifying,” I gasp. “So that’s your man from The Office.” Butterworth grins, enjoying the moment. We are so accustomed to seeing Crook as an affable, slightly hopeless figure, most recently in Detectorists, that he’s not someone in whom one can imagine horror and annihilation residing. Butterworth was inspired after seeing him in The Recruiting Officer at the Almeida Theatre, in which he was a tough-as-nails sergeant-at-arms. “It showed a side of Mackenzie I’d never seen before. So I knew he had this in him.”

The last thing that interests Butterworth is creating the sort of historical drama you’d see on the History channel: “I wouldn’t get involved in that for one minute. In the same way that Apocalypse Now doesn’t tell the story of the Vietnam War, it’s interested in something else.” That something else, the simple driving idea, is: “Are we making our own choices or are we part of a larger pattern that is written for us? It’s that simple and is, I think, the basis of lots of our lives.”

He wrote the first series with his brother, Tom. They’re already writing the second series, joined by the third of four brothers, John-Henry. (Fourth brother, Steve, is a film producer.)

We talk about death and loss; the “enormously comforting” solace of reading great writers express grief; the communality that comes with the sense of a devastating experience shared across the great span of centuries.

When his sister, Joanna, died of brain cancer at 48, the age that her little brother is now, it was the revelation of her funeral that helped him come to terms with her death. The idea – through meeting people from all the different aspects of her work, school, friends – of the largeness of the life that she had lived.

“Although she was the oldest, she always played the youngest. She’d be as silly, giggly and foolish as can be. But at her funeral, I met lots of people I’d never met before who knew her. To the students from Lamda [the London drama school where she worked as registrar and where a scholarship fund has been set up in her name], she was absolutely a mother. No foolishness there, but a pure sense of warmth and provision. To her colleagues, she was terrifying. With her friends, she was the coolest one among them. So you had someone whose life had been cut short but who’d been these very different people. I’d only seen one side of her and it was a thrill to discover she’d lived all these other lives. She was amazing.”

Their childhood home was in St Albans on a 60s housing development; the boys in bunk beds, huggermugger, in a shared room. Their parents were born part Irish-Catholic; Butterworth Senior a truck driver who’d won a trade union scholarship to Ruskin College, Oxford and qualified as a lecturer in industrial relations and economics. He was 19 years older than his wife, whom he’d met when he went to her home to fix her gutter.

Having read about the mess of broken-down vehicles outside their house and the tribe of children, I wonder if it was a bit like the Larkins in The Darling Buds of May? “It wasn’t as industrious as that… It was kind of just… Kids came in and they didn’t come out. Growing up, there were lots of books around and certainly a sense that you could do pretty much what you wanted. It was odd, on the days my father could be bothered, there were rules – and on the days he couldn’t be bothered, there weren’t. It was a bit difficult – boundaries were an issue. In a class of 30 people [at the local all-boys’ comprehensive school] everyone was having different experiences but none resembled ours.”

He was in a group of boys at school where fighting was considered cool and when he went on to read English at St John’s, Cambridge, he boxed for the university; his favoured analogies are sporting.

We’d started the interview talking about his only showbiz fight, which was with Harvey Weinstein. The only time they worked together was 17 years ago on a Miramax film called Birthday Girl with Nicole Kidman that Butterworth directed. The fight was a street brawl and was over Weinstein’s insistence that the producer be taken off the film; Butterworth insisted that he should not.

When Weinstein punched the producer, Butterworth punched him back – “If Harvey wants to start throwing punches, he should know that I know what to do!” Half an hour later, they were all in Elaine’s [Manhattan restaurant] sitting at the table meeting Nicole Kidman.

Weinstein also prompted Butterworth to make a rare appearance on television. He’s been camera shy since first experiencing huge success with his debut play, Mojo, which premiered at London’s Royal Court Theatre in 1995 and won numerous awards. He was 25 and it took him seven years to embark on his second play. “The next thing I did was just run away as fast as I could. For seven years I was just in Camden and Primrose Hill and I didn’t want to be famous. I had no interest in that at all.”

Since writing Jerusalem, every time there’s been a subject relating to England or the English, he is asked to opine. On every occasion he’s declined, but when the stories about Weinstein emerged, it was “the very first time that I’ve thought it was worth commenting”.

His original intention had been to find somewhere to publish a letter to Weinstein expressing his condemnation of his treatment of women. It was his university friend, James Harding, the best man at his wedding and then the Head of News at the BBC who persuaded him to read the letter aloud, then be interviewed on Newsnight. “I was absolutely fine with it because if ever there was a subject worth speaking to, it’s that.”

The Weinstein story has had a dramatic domino effect, toppling men who have behaved badly and worse from the highest perches in the entertainment world and beyond. “At the moment, the only thing that is important about Harvey is what he did to those people. If you bully all day long, you are a bully. If you do what he did, then you’re a sex offender. Being a sex addict and raping people are different things.”

When Butterworth and his partner, Belfast-born actress Laura Donnelly (who plays Caitlin in The Ferryman; the couple met when she starred in his play, The River, alongside Dominic West), aren’t in their London home, they’re on the farm in Somerset. She’s expecting their second daughter any time now and their first, Radha, is 18 months old.

Last month, when he received the Evening Standard award for best play for The Ferryman, he said he wanted to do more than dedicate it to Donnelly; he was giving it to her. The play is set in Northern Ireland in 1981 at harvest time on a farm during the period when Bobby Sands and nine other political prisoners starved themselves to death. He made the gesture partly because, as he said, “I mined your family – it was your uncle that went missing.” Partly because she did the run until she was six months pregnant. Partly, one assumes, because he loves her.

Soon Butterworth will be the father of four daughters and there are no complaints from him. “I’m one of four boys and having now had three girls and one on the way, I love it,” he beams, “and I feel absolutely blessed.”

Britannia starts on Thursday 18th January at 9pm on Sky Atlantic