It’s hard to believe that in real life the youthful-looking actor and musician who plays him will turn 38 in just a few weeks, but Johnny Flynn smiles: “I’m lucky with my looks.” However, looking a little embarrassed, he admits: “It didn’t feel very lucky when I was 21 and graduating from drama school, because I was being offered the roles of 12-year-olds. “But it’s come around with the Bowie film, and I was grateful that I was able to make it work. Of course, it’s all going to come crashing down on my head one day, but I’m making the most of it while I can.”

The son of the late actor and singer Eric Flynn, he grew up watching his father cheerfully navigating the ebbs and flows of a performer’s career while never losing his enthusiasm – a career into which Flynn never questioned he would eventually follow him.

He is also half-brother to Jerome Flynn – the star of Game of Thrones, Ripper Street and Nineties TV series Soldier, Soldier, who turned his partnership with fellow on-screen squaddie Robson Green into pop stardom as Robson & Jerome – so he knows all about the vagaries of his chosen profession.

“I was a music scholar as a kid,” he explains. “I played the trumpet, and I was a choir boy, and I had violin lessons, oddly enough, in the house that Jane Austen had died in, which was a spooky idea to a six-year-old kid, because you think you’re going to open a closet and find Jane Austen’s skeleton or something.”

As a teenager, growing up in the cathedral city of Winchester, Flynn loved music, but was also beginning to be attracted by his Dad’s other great love – that of the theatre.

“I liked the idea of doing plays at school but I wasn’t allowed to do those because they rehearsed at the same time as orchestra practice,” he smiles. “But meanwhile, I’d discovered literature and poetry through the English Department, and fallen in love with that, too.

“I loved the types of stories I realised I could tell after I discovered Shakespeare and Pinter. So when I left school, I went to drama school, which was an act of rebellion at the time, because I was supposed to go study music.”

Not, he adds quickly, that he left music behind when he went to London’s Webber Douglas Academy of Dramatic Art.

“I was running club nights with bands at the same time that I was doing plays. And I busked too – I had to because I was so broke,” he says.

“Just to be able to afford to live in London, I had three jobs, and I’d be busking on the side to get £15 together to buy lunch or a cup of coffee, and then I’d go to an audition and turn up with my guitar on my back from the busking.

“The first audition I went to, they felt sorry for me because I looked like a tramp – which is, basically, what I was.” In a way, Bowie is the perfect role for the multi-talented Flynn.

Stardust imagines a doomed three-week promotional trip the young singer made in 1971 when trying – and failing – to break America with his third studio LP, The Man Who Sold The World.

Despite contact lenses and fake teeth, some critics have unkindly remarked on the fact that Johnny is not the spitting image of Bowie.

Such is the ardour of some fans that he has been attacked online, having admitted: “I’m convinced that people are innately good, but this period has been tough for that perspective. I’ve been attacked online, sometimes quite violently, you know, people saying, ‘Let’s go and string up Johnny Flynn, let’s go and beat up Johnny Flynn’.”

He has explained previously: “I don’t actually want it to be that kind of pristine impersonation because firstly, that’s not a soulful, inhabited, real performance necessarily. And I’m not an impersonator, I’m an actor.”

Things haven’t been helped by a tweet by Bowie’s son, film director Duncan Jones, stating: “This movie won’t have any of Dad’s music in it, & I can’t imagine that changing. If you want to see a biopic without his music or the family’s blessing, that’s up to the audience.” 

However, the brouhaha is unlikely to affect Flynn’s career. He is about to star as Dickie Greenleaf opposite Andrew Scott’s calculating Tom Ripley in a television remake of Patricia Highsmith’s The Talented Mr Ripley, and as Ian Fleming in the wartime intelligence film Operation Mincemeat. 

Also coming up is The Dig, Netflix’s star-studded film drama about the Sutton Hoo burial find in East Anglia in which Flynn plays a dashing archaeologist.

He also finds time to perform as the lead singer and songwriter of the successful folk rock band Johnny Flynn & The Sussex Wit, he’s also played Albert Einstein on television in the National Geographic series Genius, had parts in both recent TV serialisations of Vanity Fair and Les Misérables.

And last year, he made himself really quite famous in certain quarters on the big screen by flashing his bottom as an unusually sexy Mr Knightley in the recent film adaptation of Jane Austen’s Emma alongside Bill Nighy, Miranda Hart and Myra McFadyen. “It was a nice way for the film to introduce the character,” he shrugs, matter-of-factly, of the latter scene. 

“And [director] Autumn [de Wilde] wanted to indulge the female gaze for once because obviously, women’s bodies have been shown in films so often – plus, the fact is that people didn’t wear underwear in those days, so it was an accurate portrayal of life at that time.”

A sex bomb in the making? Hardly – he will celebrate his tenth anniversary with his wife, theatre designer Beatrice Minns, and they have three children, Gabriel, Ida and Lorca whom he describes as “my world”.

“Last year, my wife and I actually celebrated our 20th anniversary of being together, which is bonkers,” he says, happily.

“We got together when we were 16 at school, and went like that for ages. Then we both went away to study – I was at drama school, she was at art school – and we did have other partners in between.

“Thank God, because she was my first kiss, and it would have been a disaster to have the eternal ‘What if?’ hanging over us if we’d only ever been with each other.”

Ask him the secret of their longevity, however, and he looks a little puzzled. “It’s strange even to think about,” he says after a moment. “I guess she’s my best friend. And that’s very grounding in this world I work in that’s quite topsy turvy and where – in normal times – there’s a lot of travelling and I’m often away. But then when I come home, she’s there and she’s really an anchor for me. She doesn’t take any bull***t, which I appreciate, she’ll just tell it like it is.

“It’s quite easy to lose yourself in the slightly ridiculous element of this job of mine, but there’s no room for that in our home life, it’s just about the kids and each other as a family, and I’m very grateful for that.”

Nevertheless, he admits, it’s just beginning to dawn on his eldest child, Gabriel, nearly nine, that dad is something of a celebrity.

“When Emma came out, he went on a school trip and saw the posters with my face on, and came home and was, like, ‘Dad, you’re everywhere’.

“And it was quite weird at the time because there’s a bus stop just outside our house, and we have a tiny crack of the window in our front room that isn’t frosted, and whatever advert is on the bus when the bus stops is looking down at you.

“When the first Emma poster on the bus pulled up, we were all sitting on the couch and we looked up and it was my face peering down. That was weird.

“But we’re dealing with it – I’m very conscious of protecting his experience of being a kid, and making sure that all of my kids have a regular childhood. Fame has its pitfalls and we’re trying consciously to avoid them.”

One of the pitfalls he is particularly keen to avoid is the trap of fitness-obsession.

“I try not to be too fit if I can help it,” he admits, frankly. “I’m bored with watching actors who look too fit anyway. If I see an actor playing a cop and he takes his top off and he’s got ripped abs, I think, ‘Mate, you’ve spent more time in the gym than on the beat’. I’m more interested in real bodies.

“Besides – I like drinking beer, and the idea of never being able to eat a potato just sounds tedious. So I think if you just eat well and cycle occasionally, you’re probably okay. Between that and running around after my kids all the time, I think I stay healthy enough.”