As the Sherlock star prepares to play a dapper 70s spook in Tinker, Tailor, Soldier, Spy, Benedict Cumberbatch tells Emma John about the joys of kitesurfing, being single and punching Tom Hardy – while presenting the sharpest looks from the coming season

Benedict Cumberbatch is talking Edwardian manners, the brutishness of croquet and a million other things that segue rapidly into each other while my brain struggles feebly to keep up. He is making me a cup of Earl Grey, and a single question – shall we share a teabag? – has triggered this rush of inspiration, from tea ceremonies to post-colonial theory. It's fair to say that Cumberbatch is both a thinker and a talker.

His features – the huge almond eyes, the sweeping Cupid's bow, the acute tapering from cheekbones to chin – can, in repose, hint at something extra-terrestrial; lit with animation, however, they're charmingly boyish. He's soon to begin shooting a TV adaptation of Ford Madox Ford's First World War novel Parade's End, hence the current obsession with Edwardian England – Cumberbatch prepares meticulously for each new role with a welter of study and likes to immerse himself in the relevant historical and cultural detail. So what, I wonder, did he do for his part in Tinker, Tailor, Soldier, Spy, his latest film? Learn Russian? Write ciphers?

He says he did go on a secret solo mission – to kite surf in Morocco. "It was the first time I'd gone on holiday on my own," he says, looking, as he says it, much younger than his 35 years. "I was in Essaouira and because my character was a spy originally stationed in North Africa, I walked the streets alone at night imagining what it was like for him – the oppressive doorways, the dark alleys."

Cumberbatch has recently had his pick of roles: starring alongside Jonny Lee Miller in Danny Boyle's sold-out Frankenstein, directed by Steven Spielberg in War Horse and cast by Peter Jackson in The Hobbit. But he has, he admits, always wanted to play a spy – "any actor worth their salt would jump at the chance", he says, "because it's all about mask shifting". His opportunity finally came thanks to Tomas Alfredson, the Swedish director of Let The Right One In, who cast him in his adaptation of John Le Carré's celebrated MI6 thriller – a film that is already being talked about in the industry in hushed, Oscar-worthy tones.

The iconic Cold War spymaster George Smiley is played by Gary Oldman – trading in his usual fire-eating performance for a cloak of impassivity – and Cumberbatch is Peter Guillam, his sidekick in all but name, who puts his own integrity on the line to help him uncover a Russian mole at the heart of the secret service. As eyecatching as the film's 70s aesthetic – gunmetal London skies, stolen documents in buff folders – are the names populating MI6's HQ: Colin Firth, Toby Jones, Mark Strong, Ciaran Hinds, John Hurt and Tom Hardy. "That's a call sheet I'm going to frame and keep for ever," says Cumberbatch.

You imagine this gentlemanly cabal of British actors convening in their trailers at night to share a bottle of malt and smoke Havanas, and while the reality wasn't quite as glamorous, Cumberbatch is visibly thrilled by the memories – reliving them with pitch-perfect impressions of his co-stars. First there's the terrifyingly laconic Oldman – at their first meeting a nervous Cumberbatch chattered uncontrollably, while the older actor silently scanned him through his sunglasses – next, it's his mate Tom Hardy, who Cumberbatch got to punch, for real, halfway through the film. "'No, no, blow harder, blow harder, it's cool, I can take it!'" rattles Cumberbatch, in Hardy's geezer tones. "I said, 'Tom, mate, it's not cos I don't want to hurt you, I just don't want to break a sweat…'"

You suspect he also didn't want to wreck his suit: while Hardy gets to swagger around in a sheepskin jacket, Cumberbatch is buttoned into sharp three-pieces. "Tom did Starsky and Hutch via The Sweeney and I got the suits," he grins. "Fuck me, those suits…" If there's plenty of competition for the best acting performance in Tinker, Tailor, Cumberbatch wins most-dapper-dressed with ease: one dark grey number with powder-blue tie and matching kerchief practically demands its own agent. "I'm hoping maybe the film's going to bring that kind of 70s suit back, you know?" he says, putting on an exaggeratedly hopeful face. "Like Keira was supposed to do for one-piece swimwear in Atonement…"

"I’d love to transform my body into a war machine. I want my Daniel Craig moment": Benedict wears shirt £445, trousers £395, and boots £445, all Alexander McQueen (alexandermcqueen.com). Model wears dress £6,350, Julien Macdonald from Selfridges (selfridges.com). Photograph: Dean Chalkley

His off-screen persona hasn't always been so stylish: "I've been quite a late developer on the clothes front, but I've suddenly realised it is one of life's joys." Martin Freeman, his Sherlock co-star, can take some of the credit. "There's a man who knows his threads," nods Cumberbatch, admiringly. "He's a very natty dresser. He gets stuff made and is always coming in with new pairs of shoes so I've been watching his clobber…" So much so that his credit card was recently declined after a birthday spree at Selfridges. "That's when I realised that I'm changing my habits!"

He looks down at the outfit he's wearing and ticks off recent purchases – the trousers ("I'm not sure the turn-ups work with these Jack Purcells," he frets), the Reiss sports jacket. "In the riots I would probably have stuck out like a dandy sore thumb and been beaten to shit."

Sherlock was shooting night scenes in north London during the August riots. Fortunately for Cumberbatch, his scenes had already wrapped, but Mark Gatiss and Martin Freeman were among those evacuated from the location shoot when gangs bore down on the set, stealing scaffold poles and smashing trucks. Cumberbatch admits, with humour and considerable passion, that the riots were a nasty challenge to his natural liberal principles. "I'm a Prince of Wales Trust ambassador, so I'm all about giving youth an education, a voice and a chance to not take the wrong road," he says. "But those eejits saying they're doing it for socio-political reasons? Fuck off, no you're not, you're on a jolly and you're getting away with it. It makes me want to belt them, make them lame for a bit so they're dependent on other people's mercy…

"It's very hard for me to talk about it," he continues, "because I came from an incredibly privileged bubble so the minute I open my mouth I can sense the comeback of, 'What the fuck do you know?' And that's fair. But my sympathy is with the people who do know what they're talking about, who have been brought up on estates and live morally decent, contributing lives and who have seen opportunists destroying all their work."

Perhaps the subject is close to his heart because he has always loved kids and young people. He's been broody "for ever" – a few years ago he said that he'd like to be a dad by his mid-30s. "Yeah, I'm a bit behind on that," he says ruefully. "Maybe it's because I was an only child, but I've always wanted kids. I've realised now that the reality of children is you have to be in the right place with the right person."

Last year he broke up with his partner of 12 years, actor Olivia Poulet; he hadn't been single since he was at university. "When I was last single I wasn't the same person, I was desperately backwards in coming forwards. But now I quite enjoy it. Naturally, I miss the proximity of a partnership with someone I know and love – and I still love Olivia to bits – but being single's fun."

It's not the only respect in which his life has recently changed considerably. A few months ago, he was offered the opportunity to star on Broadway, reprising his much-acclaimed role in Thea Sharrock's production of After The Dance – and he turned it down. "I've never really made a head-over-heart decision like that before," he says, "but there's a bit of momentum and I'd like to keep myself available for films. Because I would like to sit at the big table. I've been watching James [McAvoy] and Michael Fassbender and Ben Whishaw and I want a little taste of that…"

Having Spielberg and Jackson already on his CV shouldn't hurt his chances. Cumberbatch is keen to diversify and prove that he can do far more on screen than the rent-a-toff roles his aristocratic bearing and Harrow-educated vowels might suggest. And, as his kite-surfing holiday hints at, he's not afraid of physical adventure. "I'd love to transform my body into some ridiculous war machine," he says, with a twinkle. Don't bet against this cerebral character actor reinventing himself as an action hero, given half the chance. "I want to have my Daniel Craig moment!" he laughs. "I want to run round a desert shooting guns at aliens and looking like I barely have to take a breath. I'd love to do all that shit!"

Tinker, Tailor, Soldier, Spy is out on 16 September