Freddie Fox on playing Romeo, the appeal of gangster films, and nature vs nurture

It seems it was written in the stars that Freddie Fox would play Romeo, the star-crossed lover. The 26-year-old actor, youngest cub of the Fox acting dynasty, had always wanted to tackle Shakespeare's romantic lead: "I thought it was a part that would probably really suit me – it's a high-energy part, in a high-energy show."

Happily, Daniel Evans, who runs Sheffield Theatres, had the same thought. Fox was invited for a chat and had a feeling this might be his moment. "I'd convinced myself by the time I sat down that he was going to ask me to do Romeo and Juliet, and that I was going to say yes." Right on cue, Evans opened with: "Romeo – feel like it?"

Almost a year later, the production is about to open at the Crucible; Morfydd Clark – a young Welsh actress, most recently seen in Violence and Son at the Royal Court and in Carol Morley's film The Falling – is Juliet, and an appropriately youthful director, Jonathan Humphreys, has been brought in. Fox says he always draws on his own experience for any part, including the love-struck Romeo, but – after causing a flurry when he said in an interview this year that he could be bisexual – he's tight-lipped on the topic of his own romantic life. "It's just not a question that needs to be responded to," he says with a tight but polite smile.

Humphreys' production of Romeo and Juliet is set in a small town – "somewhere like post-breakup Yugoslavia," suggests Fox. "So you get this slightly gangland place where the Capulets and Montagues are big families; they've had a rivalry over new business contracts." Over tea at a London hotel Fox tells me Evans had been on the panel for his drama school audition at Guildhall, when Fox was 18, fresh out of boarding school (Bryanston, in Dorset), and – if possible – even more confident than he is today.

"It was awful. I made such a fool of myself! I went into the audition feeling like the Laurence Olivier of the public school system. I did Noel Coward, Bernard Shaw and Oscar Wilde – and they said surely you can do things other than drink tea and speak nicely? So for my second audition I did a piece from [David Mamet play] Glengarry Glen Ross, in my gruffest Pacino voice. Dan looked up at me afterwards and said, 'That is the most preposterous audition I have ever seen in my life.'"

One can only imagine… with his elegant good looks, Fox has excelled playing tea-drinking, upper-class types: onstage as Wilde's lover Bosie in The Judas Kiss, playing a Bullingdon Club boy in the film Posh, and appearing in BBC costume dramas such as Parade's End. Not that he can't do contemporary – he was a waspish, Mancunian-accented hipster in Russell T Davies's recent series Cucumber – but macho Mamet isn't exactly his calling card.

"And somehow I got in!" Fox exclaims about that early audition. Six years later, and Evans booked him for his first Shakespearean role, which he's loving. "I think every actor probably has a little bit of apprehension at the beginning of [their] first Shakespeare. And yet my dad had said to me many times: you will suddenly realise how blessed you are to say those words because Shakespeare makes it very easy for you."

Fox's father is the esteemed actor Edward Fox (The Day of the Jackal). Freddie is just one branch of a thespy family tree: his mother is Joanna David (Rebecca); his sister, Emelia Fox (Silent Witness). One uncle, Robert Fox, is an influential producer (Notes on a Scandal), while another, James, is an actor (A Passage to India) now appearing in the West End in Dear Lupin, with his son Jack Fox – whose career choice is shared with his siblings, Laurence and Lydia.

So, is it nature or nurture? Bit of both, is Freddie's conclusion. Certainly it was his fabulously luvvie upbringing that made him want to become an actor. "I remember [actors] Michael Stroud and my godfather John Castle, mum, dad, Phyllida Law – all these people being around me when I was little, and watching them laugh and laugh, telling all these stories, and wearing great clothes… I suppose it's what made me want to be an actor. It made me think acting was something that you were allowed to do; it wasn't a privilege – it was normal."

Of course, his upbringing sounds absurdly privileged – as Fox is aware. "Look, I certainly couldn't say that my unusual upbringing didn't lend itself to becoming an actor – of course it did. People want to see what Edward and Joanna's son can do. It will get you into a room, probably, and it certainly got me my beloved agent [who first saw him perform at a school play]. But once the door's open," he adds, "you've got to keep it open."

He does see the talent as a genetic gift, too: "Some people cannot stand up in front of people and talk, and I can – I think that's something you don't learn; you're born with it." Yet the anecdote he uses to illustrate his point underscores the value of knowing the right people.

Fox's first professional gig after acting school was in a Feydeau farce, A Flea in her Ear, directed by Richard Eyre at the Old Vic. "It was a really big, challenging part, and I said, 'Why have I got this?' And Richard said: 'When you were very little, you were at your godfather's, John Mortimer's' – who actually wrote the adaptation of A Flea in Her Ear, by sheer coincidence – 'with your mum and dad, and Maggie Smith, and me, and you'd obviously just been to see my production of Guys and Dolls. After tea you got up on the table and sang "If I Were a Bell". … That was your audition, all those years ago.'"

As well as Romeo and Juliet, Fox has two films coming out in the next year: Victor Frankenstein features James McAvoy and Daniel Radcliffe in a version of Frankenstein; but more intriguing is Knights of the Round Table, directed by Guy Ritchie. Fox says he was obsessed with Ritchie's gangster films as a teenager, and he comes out with a blast of mockney that should probably be filed alongside his Pacino impression. "I had an amazing time. I put on loads of weight and went to the gym loads, to try bulking up."

He still ain't exactly Vinnie Jones, but the Fox will no doubt kidnap the hearts of a few young audience members as Romeo. Weirdly, given his pedigree, he's the first in his family ever to play Romeo. Is that a pressure, I ask? "No no, there's no pressure – it's just an interesting fact," he grins. "I don't feel any trepidation."

'Romeo and Juliet' is at The Crucible Theatre, Sheffield, 17 September to 17 October (sheffieldtheatres.co.uk)