The Game of Thrones fanbase is easier to define by its numbers than its characteristics. The HBO show’s cocktail of extreme and indiscriminate gore, incidental nudity and fantastical elements is as enticing to some as it is off-putting to others. But the series, based on George RR Martin’s A Song of Ice and Fire, is a multi-award winner and a viewing-figure record-breaker; a sort-of catch-all masterpiece that has both Breaking Bad’s cool and Star Trek’s geeky appeal.

Whether they’re convention-dwellers or serial box-set obsessives, its hardcore viewers are as fanatical as they are disparate. Which is how Kit Harington – the London-born actor who plays Jon Snow, a survivor in a show that isn’t at all sentimental about knocking off even its leading characters – has found himself to be a genuine superstar on a global scale.

“I have to prepare myself for the madness of when Game of Thrones comes out more so than I have to prepare myself for the actual doing of it, which seems like the wrong way round, really,” the actor says, about the current fifth season.

It puts him in a strange position. To some it’s “Kit who?” while to others he’s a hero, a demi-god and a sex symbol. He baulks at the idea of being a pin-up – “I absolutely hate to think of myself as that” – but recognises it is part of his ever-growing stock. “Any actor who is taking on lead roles is probably going to have that sort of term attached to them and it’s often something that they have to fight against a lot of the time, but it’s not something that I ever think of myself as.

“It doesn’t help to sell sex, it helps to sell a story and sell a character. People are over-sexualised in this industry a lot of the time and that’s something that we, as young actors, have to really be aware of,” he adds, rather piously, given David Benioff and DB Weiss’s fondness for full-on female nudity in Game of Thrones in contrast to not much male nudity.

Sex symbol or not, Harington’s career has rocketed in the past 12 months. The actor starred in Testament of Youth, last year’s stirring first world war drama; the epic Seventh Son, which arrived earlier this year; and will be appearing in the forthcoming Spooks: The Greater Good movie.

Pompeii, his first post-GoT fame action movie, however, was something of a mis-step – a macho, all-action, no-brains thriller about the eruption of Mount Vesuvius in 79 AD – although, he’s quick to defend it.

It doesn’t help to sell sex, it helps to sell a story and sell a character. People are over-sexualised in this industry a lot of the time and that’s something that we, as young actors, have to really be aware of

“It did really well money-wise,” he says, “but it was expected to make more. I didn’t know what to expect from Pompeii. I enjoyed making it; it had an audience; and it was a really fun movie. It wasn’t trying to make any major statements about anything.”

However, playing the armour-clad lead character Milo certainly didn’t harm Harington’s rising trajectory, or that pesky status as a heartthrob. “It was a good disaster movie and I enjoyed making it. And, actually, as far as my profile went, you always have worries about movies, like how it will affect your career,” he says, still relatively nonplussed. “Looking back on it, I was on buses and billboards all over London for a month, which, whether I like it or not – and it’s not always a pleasant thing – gets your name out there. And that’s a good thing. And I was proud of it; I’m always proud of everything I do, no matter if it’s critically acclaimed.”

Apart from Game of Thrones, Testament of Youth is perhaps Harington’s finest work to date, where removing himself from his sword-swinging comfort zone has clearly reaped benefits. “It was still a period drama and set 100 years ago, but I had very much come from Thrones and Pompeii, so I did get a lot of offers for lots of swords-and-sandals movies; it was becoming a thing. And as good as some of these movies looked, I didn’t want to be that person, only ever playing the antiquated hero and playing at sword fighting.

“I love it, but I get to do that every year with Thrones, so for me, it was important to step out of that – and do something that was essentially more character-driven. “Where I am this year: I’ve done one contemporary piece, so I’m not on the lookout for more up-to-date modern films.”

He’s referring to his role in Spooks: The Greater Good, a movie spin-off of the hit BBC One series, and his first modern-day role.

“It follows on from the TV show; I play a new character who is kind of a renegade. He’s an aggressive young spy who has been kicked out of the force and now he’s been brought back in for a certain purpose,” he says. “It’s a high-octane, fun, action-packed, thriller, with resonance today as well.”

It sees him trading in the sword for the gun – but which is mightier? “A sword,” he says, “because it feels so much more natural for me. But I did spend so much time learning how to dismantle a gun and put it back together again, disarm someone, and how to fire. I got pretty proficient at it,” he adds, sounding far more sinister than he really is.

His floppy hair and well-maintained beard are part of a look viewers have bought into – even if Harington has not. “It’s so big now and takes a lot of upkeep,” he sighs, discussing his trademark hairstyle. “There’s so much maintenance and it takes a lot of time. Don’t get me wrong, I love Game of Thrones more than anything, but I wish Jon would just shave it all off.” The actor is in fact contracted to maintain his flowing locks. “There was a tricky conversation with Thrones producers that happened behind closed doors.”

After the orgy of violence that was season four – where your favourites, least favourites and everyone in between got bumped off – Harington promises season five of GoT won’t take its foot off the gas.

“The filming was pretty intense,” he says. “It was the most I’ve done for any season. So many people have died now that we’ve all been given bigger story lines. It was great; I can’t really say too much about it, but in scale it was huge, it was really huge – the amount of money, the size – it’s almost double last year.”

One thing is for sure, life won’t be easy for Jon Snow this time around. “He gets a bit harder each season because of the things that happen to him. And now he’s lost Ygritte, he hardens even more. But he’s in a really difficult place this season; he has to deal with being a politician and that’s not something he’s good at – so you’ll see his weak side.”

The show, with its depictions of violence and fantasy setting, would be an unlikely success story if it wasn’t for its quite clear appeal – it’s far and away one of the best things on TV and thus beloved by even those usually turned off by the genre. “Some people are now likening the series to sport – you don’t know what will happen next, and it has literally become a sport for a nation and fandom around the world,” he says. “It’s got to a stage now where it snowballs. Everyone who’s being told about it has hopefully now watched season four and caught up with it, so there will be more people for season five – it just gets bigger and bigger. And there is pressure there but, actually, I don’t really feel it.

Don’t get me wrong, I love Game of Thrones more than anything, but I wish Jon would just shave it all off

“If I was to think too hard about the size of it, the number of people watching it, and the importance to the future of me as an actor and what people think of me, it wouldn’t do me any good at all. It’s powerful when people come up to you. You feel it. Obviously, it has its hazards but I can’t say I have felt overwhelmed by it.”

Actors often speak of the family unit that emerges on TV sets – particularly the modern-day HBO mega shows, which can run six series or more. But Game of Thrones is a programme that has redefined the idea of main characters – just as you’re getting to really like one, they might get killed off. For Harington, it’s just another day at the office.

“Yeah, we lost Mark Stanley, who plays Grenn, we lost Josef Altin – we lost a lot of people last year. I could name loads,” he says. “You have to get used to losing your friends on this show. It was an emotional season last time. You become very good friends – but you stay in touch. I’m still very much in touch with Richard Madden after two seasons.”

Of course, there are some downsides to the show’s popularity. Harington is often confronted by fans repeating Ygritte’s famous line: “You know nothing, Jon Snow.” “That does get a little annoying,” he admits. “I don’t know why people make catchphrases out of a thing – just enjoy the line on the show!”

Snow may be one of the show’s more affable – even sweet – characters, but anyone who’s seen the actor, muscles bulging, on the Pompeii posters, will infer that he can handle himself. Through his work, he has undergone some extensive training, which includes knowing exactly what to do in a confrontation. “Oh yeah,” he smiles, “to a dangerous extent, that if I get held up on the street… I hope I won’t attempt anything. One too many ‘You know nothing, Jon Snows’ and, yeah, we’ll see what happens…”

The full interview can be found in the April issue of Square Mile. To see if you qualify for a free subscription, click here