Before I meet Daniel Radcliffe properly, I have to pretend to meet him. The actor is waiting for me in a central London hotel and I’ve been asked if I mind having a TV crew follow me to record our initial encounter. The crew have been shadowing Radcliffe for a few days, capturing a hectic schedule that involves promoting his new film What If, juggling a daunting list of commitments – preparing for stage plays; researching film roles – and, right now, filming what must surely be the most dazzling onscreen role of his career to date: meeting a bloke from the Guardian.

“Hello! Great to meet you!” says the artist formerly known as Harry Potter with actorly exaggeration, shaking my hand and welcoming me into his room. I sit down on the designated chair and we pretend to start the interview, until the cameras have slowly retreated from sight. Radcliffe gives me an awkward grimace: “Yeah, sorry about that,” he says, “they just want some footage of me meeting people to show what a press day is like.”

Of course, Radcliffe has spent virtually his entire life in front of cameras – whether they were capturing his onscreen debut as a 10-year-old in the BBC’s David Copperfield, his teen years spent filming eight Harry Potter films or his every paparazzi-snapped public movement. Like any child star, he’s had to grow up in public, which has meant having to conceal any slight streak of bad behaviour – Radcliffe admitted to having had a drink problem in 2011, several months after he’d gone teetotal – and spending an awful lot of time being asked if his career was likely to implode before most people’s has even begun.

Daniel Radcliffe in the first Harry Potter film. Photograph: Peter Mountain/AP Photograph: PETER MOUNTAIN/AP

“Which is hard to deal with,” he says, “because a lot of us already have those fears anyway: what if this doesn’t last for ever?; what if I don’t end up working in 10 years? So for other people to then be asking you about those things all the time is like having your innermost fears confirmed by somebody outside of yourself. And that’s quite a challenging thing when you’re 17.”

Today, Radcliffe still faces the same challenge: namely, trying to convince people, and maybe himself, that he’s just a normal guy at heart rather than a damaged boy-wizard. The challenge is no doubt made trickier by the fact he has an estimated net worth of $110m (£66m), according to Forbes, and he was the star of a franchise in which all eight films make the list for the top 50 grossing films of all time (the highest, Harry Potter and the Deathly Hallows – Part 2, sits at number four, with a whopping $1.3bn). Having to appear like a normal guy when you’re clearly not – and everyone wants to remind you that you’re not – is likely to be pretty stressful.

Then again, Radcliffe seems to run on stress. It’s midday when we meet and he’s already been packing things into his morning. Early on he had to see his doctor about the intense-sounding cluster headaches he gets: “You have to be on blood pressure medication and have an ECG every so often ... but don’t worry, I’m perfectly fine!” Following that he was at the US embassy for an interview, only to be told that he looked tired and not getting enough sleep – “I was like, er, thanks random fucking person who works at the embassy.”

Daniel Radcliffe as Allen Ginsberg in Kill Your Darling (2013). Photograph: Allstar/The Works/Sportsphoto Ltd. Photograph: Allstar/THE WORKS UK DISTRIBUTIO/Sportsphoto Ltd./Allstar

He doesn’t appear the least bit tired when we meet – instead he buzzes with the livewire energy of a workaholic. Radcliffe has talked of working 90-hour weeks and since finishing Potter he has thrown himself into the research-heavy role of Allen Ginsberg in Kill Your Darlings, undergone a physically demanding performance in The Cripple of Inishmaan and endured a stamina-sapping 11-month run in Broadway musical How to Succeed in Business Without Really Trying. He’s currently having to learn 50 lines of Japanese for the movie Tokyo Vice, which he thinks might be the hardest of the lot.

“I can’t even watch plays or films when I’m learning lines,” he says. “I start to think, hang on, they know all their lines and I don’t ... so I have to go home immediately and learn them.”

The Guardian film team review What If Guardian

You might assume that the role Radcliffe’s here to promote today was slightly less stressful: he plays Wallace in twee indie romcom What If, a nerdy yet quick-witted character who he admits is quite similar to himself. But playing himself brought its own headaches: “There’s something quite unnerving about doing so little,” he says, a look of panic suddenly etched on his face. “Like, is this funny? Is this enough? Will this make anyone laugh?”

What If follows Wallace’s friendship with Chantry (played by Zoe Kazan) and involves a will-they-won’t-they-oh-come-on-surely-they-would-have-by-now storyline that makes the characters in One Day seem like hot-headed slaves to reckless abandon. Chantry has a boyfriend, which makes things tricky, although that’s not as much of an obstacle as Wallace’s general rubbishness with the opposite sex, something that threatens to leave him languishing in the “friend zone”. Outside of the UK and US, the film is called The F Word – the F meaning friend, of course – and Radcliffe says the makers were considering calling it The Friend Zone outright before he stepped in.

Daniel Radcliffe and Zoe Kazan in What If. Photograph: Caitlin Cronenberg Photograph: Caitlin Cronenberg

“I was like, no, we can’t do that, because it’s not a [phrase] I love,” he says, no doubt aware that the phrase has increasingly been under attack from feminists. “The friend zone refers to a very male thing ... you never hear women say they’ve been put in the friend zone. And I think that’s because it’s just used by men who are pissed off that their mate won’t sleep with them.”

Despite sharing characteristics with Wallace, Radcliffe says he’s not nearly as useless with women himself: “No, I’m a lot better at being direct at things, I’m not good at suppressing that stuff. If I have a crush on a girl she’s going to know about it.” The girl who currently knows about it is actor Erin Darke, whose love of sports Radcliffe finds a turn on: “She’s an obsessive Detroit Redwings fan – when your girlfriend can talk shit about sports better than the men she’s doing that with, that’s pretty sexy.”

What If also features yet another naked scene – something that Radcliffe seems to be making a name for himself with – first onstage in Equus, then for the gay sex scene in Kill Your Darlings and next in the forthcoming Horns.

Daniel Radcliffe as Alan Strang in Equus at the Gielgud Theatre, London, in 2007. Photograph: Ray Tang/REX Photograph: Ray Tang/REX

“I don’t mind it, but I’d like to make clear it’s not a request,” he says, with a nervous grin. “I’m not sat there reading scripts thinking, how can I get my dick out in this one?” He admits the naked scenes have caused him to increase his time in the gym, especially since he watched Kill Your Darlings and thought, “Fuck, I’m skinny as a rat!”

With its folky soundtrack and cutesy animation – girls with big, sad eyes abound – What If is an indie film aesthetically as well as technically. Radcliffe has been a vocal indie fan since his teens, when he would turn up in the NME raving about bands like the Libertines and the Cribs in a rather endearing manner. Even today he sounds thrilled that he once got to meet Pete Doherty in a Eurostar station: “He was really really sweet. He let me waffle on for five minutes about how brilliant I thought his music was.”

Compared with most, Radcliffe’s musical education was pretty unorthodox. He was introduced to Pink Floyd and the Kinks by the driver who took him to the Harry Potter studios each day, and his dresser on Potter taught him about 1970s punk. Eventually he found his own thing and even went to Reading festival a couple of times. Didn’t he get hassled?

“No, not too much. I wore a gas mask for most of the time.”

A gas mask?!

“I was with Rupert Grint and we really didn’t want to be recognised.”

There seems something slightly sad about having to go to a music festival dressed as if you were heading to the western front. Does Radcliffe worry that he missed out on a normal teenagedom? He sighs. “I mean, maybe? I don’t know. I still got to go to Reading. I still had a great time. It’s one of those things that everyone wants to tell me I missed out on ... but I wouldn’t know, I’ve only lived my life this way.”

In 2012, Radcliffe starred in the video for Slow Club’s Beginners, in which he stumbled around a London pub, playing air guitar in the part of someone drunk out of their mind. He says he doesn’t like to talk about his drinking problems, but admits that they did inspire his performance in that video: “Of course, it would be foolish to pretend it wasn’t.” Yet when I ask if that means he’d ever been in quite that much of a mess himself during his drinking days he fixes me with a surprisingly icy stare: “Why would you ask that when you know I don’t like to talk about it?”

Radcliffe is still scarred by the fact he ever admitted to having an issue with alcohol. “If I had to give my younger self one piece of advice it would be, don’t talk about that in an interview,” he says. “Because I’ve answered questions on it for three or four years since. And it’s such an insignificant part of my life that everyone just wants to talk about.”

Daniel Radcliffe as Billy and Sarah Greene as Helen in The Cripple of Inishmaan Photograph: Johan Persson Photograph: Johan Persson

The thing is, I say, the crux of what he was saying was refreshingly open and mature: that he was cutting out all drink and drugs to avoid the cliched route of the tortured child star. “Well, yeah,” he says. “That wasn’t really a matter of maturity, it was just something I needed to do.”

It’s hard to argue with Radcliffe’s contention that everyone wants to talk about it. I wonder if he has ever Googled himself and seen the automatic search entries, but before I finish the question he’s started reeling them off: “Daniel Radcliffe alcoholic. Daniel Radcliffe gay. Daniel Radcliffe girlfriend,” he says, sighing as he does. Actually, I tell him, girlfriend is the top result these days.

“Oh great – I’ll take that, as these things go. I’m pleased my girlfriend comes up before alcoholic or gay. When I first did that, I got really annoyed for about half a minute, until I tried a few other people’s names and I found out [gay] comes up after almost everyone if they’re a man, and even some women – Florence Welch had it, and I was like, really?”

Maybe it’s a sign that a star has made it. “Probably. If people are speculating about your sexuality, then you’re doing OK,” he laughs, then says that these days he resists the temptation to self-Google as “it fucks you up. You shouldn’t be on there if you’re an actor. There’s a line in The Thick Of It – Googling yourself is like opening the door to a room full of people telling you how shit you are – and it’s exactly that. I first did it in my late teens and it was such a destructive thing for me to do.”

These days, Radcliffe says smoking is his only remaining vice – and he does much less of that since he’s taken up running in preparation to play Seb Coe in the Olympics film Gold. Running, learning Japanese, 90-hour weeks ... does he put too much pressure on himself? He says not, so I ask him about a quote in which he said he sometimes heard voices telling him he was going to fail.

“I was obviously not being literal,” he says. “But I think I have to apply that amount of pressure to myself because I want to do well. Now, maybe that’s not the healthiest way to function … but also, frankly, since the age of 20, all of the interviews I’ve done have involved people asking about my impending failure, and how I felt about the possibility of that. And so, when you’re confronted with that so often, you start to react to it. My own reaction was always to kick hard against it and think, fuck it, you might as well be bold now, make some interesting choices and see where that takes you.”

Wherever that may be, you suspect there will be plenty more cameras around – and Radcliffe won’t be giving himself much of a break.

• What If is released in the UK on Wednesday 20 August