Known for playing one of the most unpredictable, devilish and sadistically mischievous villains ever to hit the small screen, you’d be forgiven for being just a little bit scared of Sherlock actor Andrew Scott. Until he opens his mouth, that is. Cheerful, chatty and prone to bouts of raucous laughter, the 37-year old boasts the same razor-sharp wit as Moriarty – but thankfully cushions it with an irrepressible sense of warmth and good fun.

Returning to Dublin from his adopted home of London to promote his new comedy The Stag, Scott’s mischievous sense of humour is immediately apparent when he learns that we share a mutual acquaintance – last issue’s interviewee and his co-star in The Stag, Hugh O’Conor. Notoriously one of the nicest men in the film industry, O’Conor was a schoolmate of Scott’s when he became a child acting prodigy and landed roles in Lamb and My Left Foot.

“He was two years ahead of me in school,” Scott confirms, before adding with a devilish grin, “He used to walk through the hallways, pushing children out of the way! He was parading himself around the school, like some sort of rapper – some rapper from Ranelagh.”

With bling. I can definitely imagine sweet little Hugh O’Conor with bling. “With bling, and a grill! Couldn’t understand what he was saying.”

But while MC O’Conor was, ahem, terrorising the halls with his new-found fame, young Scott was attracted to acting for a much simpler reason: believe it or not, Sherlock’s own ‘Mr. Sex’ used to be a retiring type.

“When I was a kid, I was very shy,” says Scott, smiling at my surprise. “Not so much now, because I’m kind of used to it, and you think, ‘there’s nothing really to be scared of’. But, there’re some things that kids really, instinctively either want to do or really don’t want to do. I used to teach drama and mentor at this thing called IdeasTap, and when I’d teach kids, they’d be really, really shaky. Just having to get up and do a little improvisation, or a poem in front of twenty people is terrifying when you’re a kid. But they would be glowing afterwards. I remember going to drama classes myself, and being so shaky beforehand – and I would literally be so excited when it was over. Every week I would be like, ‘I don’t want to go, I don’t want to go’. But then I’d be like, ‘That was amazing!’ And that went on for years.”

The intervening years, since those early drama classes ended, have seen Scott carve out a fiercely impressive career path. Dropping out of his drama degree in Trinity College to join the Abbey Theatre, he focussed on theatre for a long time. He starred opposite Julianne Moore and Bill Nighy on Broadway; was central to the Olivier Award-winning production of Cock alongside Ben Whishaw and Katherine Jenkins; and he won an IFTA for his performance in Eugene O’Neill’s Pulitzer Prize-winning play, Long Day’s Journey Into Night. When he did venture into television and film work, his roles were interesting, diverse and – importantly to Scott at the time – not too visible.

He played small parts in Band Of Brothers, Saving Private Ryan, Lennon Naked in which he did a memorable Paul McCartney opposite Christopher Ecclestone’s John Lennon, The Hour and John Adams, opposite Paul Giamatti and Laura Linney.

But it was his performance as Moriarty in BBC’s wildly successful television show Sherlock that thrust Scott irrepressibly into the limelight. Appearing in a 2010 episode of Mark Gatiss and Steven Moffat’s drama, no-one expected that the handsome, softly-spoken Dublin boy would transform into the mercurial force that is Jim Moriarty, Sherlock’s most feared adversary. Though the brilliant, brotherly love/hate dynamic of Benedict Cumberbatch’s Sherlock and Martin Freeman’s Watson had captured the public’s heart, it was Scott’s tempestuous, flirtatious and ferocious villain who got them in their gut. The final episode of Series 2, which delivered an epic and seemingly deadly showdown between Moriarty and Sherlock, garnered nearly 10 million viewers, and social media platforms were hijacked by fans, desperately speculating as to the fate of their favourite villain.

For those hoping to learn about the innermost motivations of Moriarty, prepare to be disappointed. Even Scott prefers to keep him a mystery. He confesses that he never worried about creating a backstory for the enigmatic character.

“That’s the way I work,” he reveals. “Even in theatre, I’m not a big ‘backstory’ person. And what’s scary about Moriarty is that we don’t know his backstory, anyway. So it reduces it immediately. So even if I were to think, ‘Oh he was born here, and he had this and this happen to him’ – what’s scary is that you don’t know. If you see somebody frightening on the street, if you’ve got information on them, that’s power – power that you have. But you’re powerless when you don’t have information. So there’s no reason to create a backstory. And I’m afforded that luxury especially because the writing is good. If the writing was dodgy, you’d have to ad hoc it and manufacture some motivations. But it’s all on the page.”

Fans will also be disappointed to hear that banter between Scott and Cumberbatch onscreen, often laced with a subtle (and sometimes not-so-subtle) sexual charge, is also completely scripted, and not the result of some lust-fuelled tension between the actors.

“No!” he laughs uproariously. “That’s them. Steven Moffat is just a genius writer.”

Scott does admit to harbouring a deep-seated admiration for Cumberbatch, with whom he has crossed paths many times, navigating the theatre scene in London. The two share a relentless work ethic and a desire to take on challenging roles.

“I’m really delighted for him, because he’s a proper actor, you know? He’s done lots of different things. He worked for years, in his twenties, in theatre, TV – and films that not many people saw. He’s interested in the script, he knows about timing, he knows about pathos, he’s interested in the work, and he’s brilliant as Sherlock Holmes. He’s fantastic.”

Like Cumberbatch, Andrew Scott isn’t in the business for the fame, but because he loves the work. However, fame is something they’ve both had to get used to – to an often extreme degree. Having worked for so long without ever really having to worry about being recognised in the street, Scott now has to cope with hysterical fans, who seem to come in two forms: obsessive or really obsessive. It’s a level of fame and adoration that many actors desperately crave, but Scott is wary of the way the gawking public can treat him.

“I don’t take it seriously,” he insists. “I deal with people in the same way that I’ve always dealt with them. You know, the only thing that bothers me is rudeness. Rudeness is something that always makes me angry. I just think it’s rude to be on a Tube and stick your phone up to take a photo as though I’m an animal in the zoo. And I think it’s ruder when you try to do it on the sly, because, you know, I would always say ‘yes’! So it’s that thing where it becomes a little bit dehumanising.

“For the most part, people are lovely,” he adds. “Genuinely. But, rudeness is rudeness, whether it’s an actor being rude to a member of the public, or a member of the public being rude to the actor. It happens both ways. So I’ve had to sort of learn, recently, to make my point. Sometime you’ve got to say, ‘look, please stop’.”

Good lord: I can’t imagine surviving having Moriarty give out to me in public. Afraid that he’d skin me, I think I’d die of fright.

“You have to!” he exclaims. “One thing I’ve said a lot is that I don’t want people to become the enemy. I like people, I like talking to people and I like being able to go, ‘Hello, how are you’ and to have human interaction. So when somebody just sticks a phone in your face or when somebody is like, really hysterical, you kind of think, ‘Well, this really has got nothing to do with me’. So it’s weird a bit.”

During a recent appearance on The Late Late Show, Scott also addressed the weirdly sexual attention that Moriarty attracts, and the mountains of fan ‘faction’ and fan-made sex-scene compilations that he receives.

“There’s a sort of a new dynamic that happens with fans now,” he explained bemusedly. “They send you these, eh, short films? Where they take love scenes that you’ve been in, in the past, and love scenes that someone else – Benedict for example – has been in, and they put them together, and they give them to you. And they’re usually very shaky, shy hands, but then you watch them and you think ‘Jesus Christ!’”

Telling the story to Ryan Tubridy, Scott was laughing – but I wonder if it doesn’t feel more intrusive than he lets on? If, for example, it was an actress revealing that male fans were sending her home-made pseudo-porn and openly telling her that she was the object of their sexual fantasies, would it be as amusing? Or might we not consider it a form of horrible sexual harassment?

“I suppose, it’s part of the same world of being objectified,” Scott muses, taking a moment to think. “I’m about to play a rock star in the theatre, and the play is very much about the nature of fame, so I’ve been thinking about it an awful lot recently. To idolise somebody and to put anybody on a pedestal in that way can be cruel. You’re both waiting for them to fall and it’s also sort of, you don’t give anything really of yourself. It’s like sometimes when you’re at a wedding and someone says, ‘What do you do?’ or they say that they’ve seen you in something – but when you ask ‘What do you do’ back, they just tell you: ‘Oh, it’s really boring’. And you think, ‘Why do I not get to look outward, or ask people about themselves?’ And that’s the thing you kind of want as an actor, and that’s the way I am as a person: I like asking people about their lives. As an actor, you’re required to go in. And that’s why it’s a weird job; you’re required to go in and yet you’re the one doing the talking.”

But as for taking a tumble off the pedestal of fame, Scott isn’t worried, because fame was never how he measured happiness or success.

“I think all that stuff is nonsense,” he remarks bluntly. “The only success as an actor, the only thing I really care about, is that you get the opportunity to keep doing it, you know what I mean? It’s quite a weird thing, and I understand when people say it, you know, ‘It’s great the last couple of years’ – but actually I’ve been having a really good time for ages! And that’s what I say to these people.

“The stuff that I really remember is the stuff, when I was 19, at the Abbey. Or shooting an independent film that nobody has ever seen, in 2001. Of course you want to get a nice paycheque – who wouldn’t want to get that? – and it does help if your profile is a little bit higher. But there are actors who work their whole lives, and they don’t ever do an interview, or are never on the cover of a magazine, and they have a really good time. So, I don’t feel like, ‘Oh God, if this is all taken away from me’ and all that kind of stuff – I’ve lived in poverty before, I can do it again! I just sort of feel like, ‘Oh cool, I’m still getting to do it’ and I’m still getting to do more different stuff than ever before.

“I think you’ve got to be really careful with that success stuff. Particularly with something like Sherlock, because I don’t feel like a pressure to go be in another television programme. I’ve just been asked to be in an American TV series that would have been big, but I don’t feel like I want to be in another television series because, it’s more of the same. I want to do something different. It’s not about the size of the project. Though I’m really enjoying being in the Frankenstein movie, because it’s so different. You go, ‘Fuck, this is Hollywood! Here we are in Ealing Studios, and it’s really exciting, and there’s a huge crew and huge explosions and it’s so fun!’ But that’s fun because I’ve just come off a Ken Loach film, where it’s completely the opposite. Getting to do all that stuff is just what I want to do.”

Coming back home from the madness of London, Scott seems delighted to be promoting John Butler’s comedy The Stag, which allowed him to drop Moriarty’s maniacal laughter and take on the more grounded role of Davin, who’s organising a stag weekend for his oldest friend Fionnan (Hugh O’Conor). The warm, light comedy also stars Peter McDonald as Fionnan’s nightmarish brother-in-law to be, and Amy Huberman as the bride. As the men embark on a camping weekend, the film gently confronts not only the bizarre nature of ritualised masculinity, but also examines the very realistic struggles facing young Irish men: Brian Gleeson’s character is suffering badly after the recession; Micheal Legge and Andrew Bennett can’t get their families to accept their relationship; Peter McDonald is facing divorce; O’Conor is mocked for not being your typical ‘man’s man’; while Scott’s Davin is a commitment-phobe, nursing some well-hidden heartbreak.

“I recognised all the characters,” he says. “I read the script and I just thought, ‘Brilliant, it’s an Irish film about Irish people, that I really can relate to’. It’s absolutely for an audience to enjoy. It’s witty. I know it’s called The Stag, but they did some test screenings, and women go for it more than even the men do. It’s about male friendship, and all that kind of stuff. The guys who did Your Bad Self got together, and we all sort of knew each other: I’d worked with Pete before and I’d worked with Andrew Bennett before, and of course I knew Hugh, Ranelagh’s It Boy…”

Scott admits that stage roles are usually far more complex than their screen counterparts, and that Hollywood often reduces its male characters down to boring archetypes – not least in films about stag parties or “Boys’ Nights Out”, where the only accepted activities for men are to get slaughtered, have a hilarious encounter with a prostitute and possibly distress some wildlife.

“It always seems to be about ‘who can drink the most’ and I don’t really know very many guys who have stags like that. And the women are always really sensible. It’s boring! This thing of ‘before you’re chained up’ by your wife or your husband – I know people now where they have stags or hens, where they invite other mates, men and women. Why would you just invite your female friends or your male friends? I don’t know. I suppose the original idea of the stag is that you get together and you reconnect with the people who have formed you, before you go on to the next phase of your life, which is what takes place in The Stag.”

Scott looks up at the film poster – which, I note, sees all the other cast members wearing terribly unflattering hiking gear and furry hats, whereas Scott gets away with donning a rather stylish jacket and scarf combination. Not to objectify the poor boy further, but was that decision possibly based on cashing in on his sex appeal? Was there a PR agent in a board room arguing "We can’t put Moriarty in a stupid hat – this is Mr.Sex! We can’t put fur on his head!"

Scott laughs uproariously. “Exactly! ‘We’re not putting a woolly fucking hat on that!’ I actually wanted to try on a hat, and I literally put it on and John Butler, the director just said, ‘Take it off’. I asked why!”

Because you’re the money, darling. “Show them the face!”

Filming The Stag also gave Scott the chance to spend some time at home, after living in London for almost eleven years. He admits that after living away for so long, his sense of home is divided between the two cities.

“England doesn’t feel like home, but London feels like home. Dublin also feels like home. I know it like the back of my hand, I know everything about it. But I hadn’t worked in Ireland for, like, four or five years and so I really loved doing The Stag. One, because it was a great project, and it was really funny and stuff; but it was also about Dublin, and Dublin guys that I recognise. So there’s something really pleasurable about, in a way, not really having to act. I do a lot of stuff – I’m doing posh, and I’m doing American, and you do lots of different voices and accents and backgrounds and I love all that, but there was something really nice about playing a guy from Dublin. And that, sometimes, can be the hardest thing – just being yourself.”

But ironically, it was trying to perfect a foreign accent that resulted in Scott’s most personal revelation. Appearing in BBC’s TV film Legacy, his role as a Soviet diplomat called for a Russian accent. Finding it difficult to uncover footage of a native Russian speaking in English, he resorted to watching videos of Vladamir Putin for research – but when Putin’s domestic policies became increasingly focused on promoting homophobia, Scott dropped his study – and began to speak out. In an interview with the UK Independent, he used a discussion about his research methods to professionally come out, acknowledging that “Putin introduced anti-gay legislation this summer – so, being a gay person, I switched to Rudolf Nureyev videos instead. It was another Nureyev defection of sorts!” In his typically charming, witty way, Scott had decided to make explicit something he had previously kept quiet about in the press.

“I’d spoken about it,” he reflects, “but it’s not really something journalists picked up on. When I do interviews now, they’re read by more people, so I kind of knew that he was probably going to pick up on that. It’s like I always say: it’s not a talent, it’s not something to be proud of or ashamed of, it just is. But it’s interesting; it’s important for me to say that, for young actors, it hasn’t affected my career in any way – in fact, the opposite. I think something that people respond to, in anybody but particularly in artists, is authenticity. That person is who they are, and people pick up on that. That’s what I mean by, ‘Be who you are so you can be who you aren’t.’ There’s a difference between privacy and secrecy, and I do think it’s important to go, ‘That’s for me’, but you don’t want to be like, ‘That’s something I can never talk about’ – because that’s toxic too.”

Though based in London, Scott says that The Stag director John Butler along with his friends and family back home have been keeping him up to speed on Ireland’s current debate regarding homophobia; a conversation ignited by an RTÉ interview with drag performer Rory O’Neill, aka Panti Bliss. Scott is clear in his take on homophobia.

“You don’t have to spray paint somebody’s car, or throw a beer can at them on the street, to be homophobic,” he says forcefully. “It comes in lots of insidious forms. Homophobia is about saying that gay people have less rights than straight people. That’s the end of it.”

He also expresses admiration for Panti Bliss’s ‘Noble Call’ speech.

“I thought it was brilliant what Panti said, which is now homophobia is something that is being embraced by homophobes! What was that thing she said, which was like a neat, Orwellian trick? I thought that speech was extraordinary.”

He stops for a moment, before continuing, thoughtfully.

“I don’t think that people are intrinsically homophobic, because otherwise we’d have to give up. I think people are ignorant, and there’s a lot of work to do. But it’s also very important for me to say that, I wasn’t bullied, it never affected my career, my parents were great about it. I mean it was always easy for them, and when I was younger, I still had feelings of isolation and shame, and that was compounded by a law that backed up that feeling. And so, in ridding ourselves of that archaic law, you free up that mind space for young people, so that they can focus on all that stuff they should be focusing on, and allowing them to be outward looking. When someone is outward looking, rather than inward looking, it means that they become kind and generous and thoughtful people, and that’s what makes people happier. That’s why it’s a human rights issue.”

Utilising his platform as an actor to address LGBT issues, Scott is incredibly enthused about starring in Matthew Warchus' upcoming feature Pride, the true story of an unlikely union between Welsh miners and the LGBT community in 1984.

“I play a Welsh guy called Gethin, who was part of a group called LGSM. That’s with Bill Nighy, Dominic West and Imelda Staunton. Incredible cast, and I think that could be very exciting. And Ken Loach’s Jimmy Hall is coming out too, I’m dying to see that. To be honest, I’m currently really looking forward to going back to the theatre to do this rock star thing. I haven’t done a play in a couple of years, and I’m in the process of learning 120 pages of dialogue, because we start rehearsals next week.”

Not to mention, he’s also in the upcoming adaptation of Frankenstein, starring alongside Daniel Radcliffe and James McAvoy. And of course, there might be a return to Sherlock – though under pain of death, he’s keeping his lips sealed on that one. Either way, he’s excited...

“They’re all varying degrees of intensity, bigger parts, smaller parts, and they’re all very different – so they’ll all have different audiences. But I love working. There's definitely an obsessive streak. You know it’s that thing, as an actor, and maybe even a person, I resist definition, I think. I like the idea of being able to do different things. The thing that would scare me the most would be being forced to stay stuck, to just to be one thing.”

You know that’s going to be my headline now, I tell Scott: “I resist definition.”

That maniacal laughter is back. “Yeah!” the actor exclaims, putting on a very serious, tongue-in-cheek, thespian voice. “‘I resist definition.’”

Indeed he does.

The Stag is in cinemas now.