If you are the world's most famous teenager, the speculation that swirls around you is often less interesting than the reality. For instance, Daniel Radcliffe is not gay, but he does have an interest in cross-dressing: "The one piece of advice I would give to any actor is, if you want to go out on the street without being recognised, without even being looked at, go out with a 6ft 8in beautiful transsexual," he says, eyes wide. "No one gives you a second glance. Especially when you're 5ft 5in. I'd love to play a drag queen or transvestite, but not just because of the costumes. Wait, what am I saying? Yes, because of the costumes! If the script was good - I wouldn't just do it because I got to dress up. Although I maintain that I look good with eye make-up. And I'm not going to be an emo kid, so the only other option is drag queen."
To answer another rumour: Radcliffe has not had beer made by monks drafted on to the Harry Potter set. "I don't drink beer as a rule." He prefers whiskey sour or tequila. "I love tequila - it's one of those things, like Jägermeister, where you get a very specific type of drunk off it." He hasn't recruited the SAS to walk his dogs, either, or ever grown eight inches in two months ("I wish!"). "And the best one: I had a nude sculpture made of myself to put in my living room. I don't know how big they think my ego is."
It is no surprise that Radcliffe, now 19, is a target for the tabloids. Last year he reportedly signed a contract worth £25.6m for the final two Harry Potter films, and was ranked as the world's highest-earning tween, alongside Disney star Miley Cyrus. Has he ever had to sue the press for defamation, or threaten to? "We've got involved a couple of times," he says carefully, "but it's never got to court. We've had to be very vigilant." He also has to be alert to entrapment, though it helps that he's not a regular club-goer, preferring "old man's pubs" and the odd gig. (He loves indie music, from Radiohead to the Hold Steady.)
"There have been people who have tried to exploit me. You get chancers out there who just want to make a quick buck, but as long as you tune into them and who they are ... The best thing I've learned is, if you're going out, never go out alone - you leave yourself vulnerable. If you've got someone else there you trust, they can say, be wary of that person. I probably used to be too trusting of people."
A while back (he thinks it was when he was 14, while filming the third Harry Potter film), Radcliffe made a choice that he definitely did want to be an actor when he grew up. "When you're in the position I'm in, you have two options: you can either shut yourself off from everybody, from the world, and not live a full life. Or you welcome everybody into your life and occasionally somebody will try to take advantage. And I'd much rather be that person who lets people in. Because, as an actor, people are your greatest resources."
This is why, on the evening I meet Radcliffe - Dan to everyone he knows - I find him busy people-watching. He's arrived early for our interview, at a private London club (his PR is a member, he's not), and has been taking in the clientele, trying not to gawp at Christopher Biggins. "And there was this wonderful man downstairs who was flirting so overtly with any female waitress that passed him by. It was fantastically funny to watch. And one day, when I'm 40 or 50, I hope to be playing that part. I'll remember this ... "
Despite all the pressure, it seems that Radcliffe is growing up sensibly. Normally, even. He loves cricket, likes a drink and a furtive smoke, and watching bad TV on a Friday night in his underpants. He has a girlfriend he met at work. He's bought a flat near his parents' home in Fulham, and has lived alone for 18 months. Mostly, it's going well: he keeps his flat fairly tidy, although he's still taking washing to his mum. "Is that shameful?" he asks. "Not every time! But occasionally, if it's a big sheet or something." He's not fond of ironing, as his scruffy outfit suggests. "It's when you get to a zip or a button and you think, 'What the fuck do I do now?' The thing is, I think things look good creased. Scruffy is in now," he says hopefully. "Ironing boards are a classic example of something I find horrible about modern society: the excitementation, for want of a better word, of mundane things. Funny ironing board covers - I hate them."
Radcliffe is a thinker. Referring to the Potter films, which have overtaken James Bond as the most successful movie series in film history, he prefers a different comparison. "You know what I take pride in more than anything else about these films? They're the only films since Truffaut's Antoine Doinel series that have featured one character going from about the age of 11 to 20. To be in Truffaut's company, I'm happy with that."
He is also a fan of modern art. For his 18th birthday in July 2007, when his protective parents notionally handed him financial freedom, he thought about treating himself to a car (nothing too flash - a Toyota Prius, say, or a Golf GTI); two years on, he hasn't even had a driving lesson, much less splashed out on some wheels. Instead, he bought a work by New York-based artist Jim Hodges, which is how he was introduced to the world of transvestites. "The dealer said they wanted to sell it to a more prestigious collector, and Jim got word of this. Turns out he's a massive Harry Potter fan and insisted they sell it to me. Ever since then I've been really good friends with Jim and his best mate Tim, a photographer. And they are two gay guys, artists, in New York, and they introduced me to these amazing, crazy, mad, weird, extraordinary people. I was immediately embraced by the New York tranny community!"
The Hodges work, Mona D, Mary And Me, is "basically a drawing of blue ink on white paper. And it's the words, 'Oh for crying out loud' which is something his mum always used to say, as I think probably all our mothers did. And in the midst of it, it's weirdly calligraphic." What was its appeal? "I suppose - without meaning to sound like it's a link to Harry Potter - it's about finding something magical and fantastical in a mundane phrase. That's what's lovely about it."
He's a big reader, too, and talks enthusiastically of a project in his dressing room, a wall-mounted display of "the most important authors from the 1700s, 1800s, 1900s and a few from the 21st century. It was fantastic - Jo [Rowling] walked in, and the first people she picked out were George Eliot and Joseph Conrad. And Nabokov." He is also a keen poet, though admits that his early verses were all about quantity - "Now I'm lucky if I write one thing a month or every two months. But when I do write, it's of a much higher quality. It's more considered, more concise, I've got less time for the ... pretension I had early on."
He's published some poems under a pen name, and although he doesn't tell me what it is, he provides so many clues even Dobby the house-elf could solve it. It seems to be Jacob Gershon: Jacob is his middle name, Gershon the Jewish version of Gresham, his mother's anglicised maiden name. Modern poetry and free verse "irritates me", he says. "I love people like Simon Armitage. He has such an immaculate grasp of metre and rhyme, if he wanted to do poems like that, he could. But sometimes free verse, for me, is for people who can't do structure. And when I don't write in form and metre, I become unbearably self-indulgent. It's what Robert Frost said: free verse is like playing tennis with the net down."
Why does he like writing poetry? "As an actor, there is room for a certain amount of creativity, but you're always ultimately going to be saying somebody else's words. I don't think I'd have the stamina, skill or ability to write a novel, but I'd love to write short stories and poetry, because those are my two passions. There is an art to a short story. I love Raymond Carver, and Chekhov - without making myself sound more highbrow than I am!" he blusters, a reminder of the public schoolboy he was, on and off, until the age of 17. "I watch Britain's Got Talent like the rest of us."
We've met to mark the imminent release of Harry Potter And The Half-Blood Prince, the sixth film in the franchise based on JK Rowling's books. Radcliffe signed up for the series in 2001, when he was 11, and is now four months into the 19-month shoot for films seven and eight (the sprawling final book in the series, Harry Potter And The Deathly Hallows, has been split into two parts). In The Half-Blood Prince, the Potter saga suffers its first loss of a major character, with the death of Professor Dumbledore, played by Michael Gambon. Was that difficult to film? "The whole film was quite difficult, but particularly that scene. I'd never been bereaved until the end of last year, when I lost my grandmother - before that, I'd never experienced any kind of sadness. So it was very tricky. It's also a tremendous pressure, because you know that a lot of people watching the film will have felt that. I tried to play it quite quiet, because that's just how Harry is."
The film also marks Harry's second kiss, with Ginny Weasley, sister of best friend Ron. Was that enjoyable? "It was quite weird for me because I've known Bonnie [Wright, who plays Ginny] since she was nine and I was 11. Very strange. But we got through it. It was good. And it'll get a bit of a cheer from the Potter fans. But I have to say, today I saw playback of Ron and Hermione's kiss [from the final book], and it is easily, from what we've filmed so far, the biggest moment in all the films. It is," he says approvingly, "a great kiss."
He pauses when I ask if he's happy with his performance. "Six is a very hard book to film, because it was essentially a lead into seven, but no excuses. I think I came through OK. I know I have a lot more to give than I do in six. And what's great is that I did Equus on Broadway between six and seven. I feel I've developed a lot in that time."
The last time I met Radcliffe, in January 2007, he was about to begin the London run of Equus, Peter Shaffer's classic 70s play. He was cast as Alan Strang, the stableboy who, in a frenzy of sexual and religious ecstasy, blinds six horses. He also had to strip naked every night for four months. In late 2008 he did it all again on Broadway. His performance in London was brilliant. Unlike the talkative, CGI-bolstered performances required of him in Potter, he was an electrifying and very physical onstage presence - despite the slight stature to which he refers repeatedly. The mild scandal about the full-frontal nudity (Harry gets his wand out, etc) and about this children's cinematic hero playing a tortured adolescent was quickly eclipsed by acknowledgment that he could really act. The critics mostly raved. "I was a lot better in New York," Radcliffe says. "New York was a better all-round show. We all raised our game."
Alan Rickman, Severus Snape in the Potter films, was a big help on Broadway. He cut short a holiday in Connecticut to visit Radcliffe and give him some pointers on stage presentation "that absolutely saw me through the last six weeks of the run" - how to be still, exploiting his "quite short and compact frame". Radcliffe says he used to "struggle" with Rickman: "I never used to know when he was joking or not. I think I took a lot of his sarcasm seriously. But recently I've woken up to it and he's actually a great guy."
Gary Oldman, who plays Sirius Black in the Potter movies, is one of the many older actors and crew members whom Radcliffe counts as close friends and mentors; Kenneth Branagh, who first floated the idea of his doing Equus, is another. Oldman applauds Radcliffe's "fearlessness" in taking the role. "To - no pun intended - expose himself. Not [just] physically get naked, but be vulnerable like that. To all the guns that could have shot him down. I think that alone is a great achievement. And he's serious about acting."
Equus was good for Radcliffe in many ways. It's how he met his girlfriend, Laura O'Toole, a fellow cast member, although he'd prefer not to talk about her. "She's just a normal person and she's not out for anything else. Which is very, very good. I seem to be a long-term relationship kinda guy. In my head I'm Byron, spreading failed romance ... There's a great line in Thackeray, 'Yes, I am a fatal man. To inspire hopeless passion is my destiny.' That's the image I have of myself [but] it isn't even remotely the case. I am quite a romantic."
It was important to be taken seriously as a stage actor, too. An only child, he was taken to the theatre regularly by his parents - Marcia Gresham, a casting agent, and Alan Radcliffe, a literary agent - and it was an encounter with the film producer David Heyman, a family friend, at a West End production of Stones In His Pockets, that led to him being cast as Harry Potter. "He was endlessly curious, and he was ambitious for his craft," Heyman says. "One of the things I respect most about him is he has pushed himself to get the most out of every moment in his life." This includes "getting everything he can from the directors" on the Potter films, among them Chris Columbus (Home Alone), Alfonso Cuarón (Y Tu Mamá También), Mike Newell (Four Weddings And A Funeral) and David Yates (TV's State Of Play).
Heyman is one of a close-knit group around Radcliffe who have protected, advised and helped keep him balanced. His long-standing PR chaperone no longer sits in on all his interviews but remains a key figure, as do his parents - his father gave up his work to become, in effect, his manager. He also mentions Sue Latimer, an agent and an old friend of his dad's, as one of "the fantastic people around me" who have made sure he doesn't wobble off the rails like so many child actors. "I've known Sue's son, Freddie Highmore - who played Charlie in Charlie And The Chocolate Factory - since we were little. She always looks out for my best interests. And then I've got the people on set. At 11, when I was first on Potter, I remember saying to everyone, if I get cocky, you have to tell me. And they always did."
One of his best friends is Will Steggle, a fortysomething father who works in the series' wardrobe department. "And because Will is a cynical man, he has put me off pretension at every stage. It is totally possible for an actor to be involved with the crew and have a chat with everyone, and be really good friends with them, then go on and do a scene. That should be your job."
He proceeds to tell me the people he "absolutely loves" on set: Rupert Grint, who plays Ron Weasley, and Emma Watson, who plays Hermione Granger. "They are, to all intents and purposes, my brother and sister." Are they all best friends? "Probably not, only because we don't see each other out of filming. But someone like Tom Felton, who plays Malfoy, I'd count among my really good friends. I went to the cricket with him on Sunday."
Big public events can be perilous. At the cricket match a man yelled, "Where's your wand, Harry?" which Radcliffe notes was "not original, not funny. Affectionate, slightly." Then there was his experience at a Red Hot Chili Peppers gig a few years ago. He was standing on the side of the stage when word passed through the crowd. "Hyde Park, 10,000 people chanting, 'There's only one Harry Potter!' It's good to be the king." He grins. "That's the thing, people don't realise that moments like that, while they're embarrassing, are also really cool."
He suspects Watson has a harder time. "Not so much [with] people but with paparazzi. Generally speaking, it's so much harder for girls. Guys are naturally lazy, and we like to lie around at home, so we don't give people many chances. Whereas girls want to get out, socialise and meet people."
But Watson seems to be enjoying all the opportunities for photoshoots and red carpet premieres. "Yeah, totally, but she's much more natural at them than I am. She's more suited to being able to talk to anyone - I get very nervous about those events. She's been photographed at a lot of [fashion] things, and I think that's a world she's very interested in. I've seen some of the clothes she's designed and [they're] very good. She's very clever. Do you know her GCSE results?" His eyes boggle: "I was thrilled with mine - seven Bs, two As and an A*. I think Emma got three As and seven A*s - she's incredibly academic, it's frightening. Me and Rupert to all intents and purposes dropped out of school. And she's going to Brown." He shakes his head in admiration of Watson's place at the US Ivy League college.
After all the untruths about Radcliffe, here are some facts: he won't be going to university, not least because he won't be doing A-levels. He is intent on an acting career, has had some Hollywood meetings, and looks forward to the time, very soon, when he doesn't have to turn down scripts because he's tied up in a converted aircraft hangar in a London suburb, in a world of wizards, Muggles and owls. There are a few projects in the offing, but the only one he wants to talk about is The Journey Is The Destination, about the photographer Dan Eldon, who was killed, aged 22, by a mob in Somalia. Funding permitting, it'll be his second biopic after his well-received turn as Kipling's son in the TV drama My Boy Jack. Radcliffe's passion for the part of Eldon stems from the fact that "everyone around him was steeled and inspired by his adventurous spirit - and it's also a character that's very unlike me. I'm not that adventurous in terms of exploring the world. The freedom that he had as a character, I don't necessarily have."
Radcliffe can't ride a bike or swim, not, as you might imagine, because Harry Potter stole his childhood, but on account of dyspraxia. "Like dyslexia but with coordination. My hand-eye coordination has got a lot better. I did an IQ test when I was about seven, and I was verbally in the gifted range, but my motor skills were rated as well below average. I'm quite proud of that."
He's Jewish, via his mum. "I'm an atheist, but I'm very proud of being Jewish. It means I have a good work ethic, and you get Jewish humour and you're allowed to tell Jewish jokes. For instance: did you hear how copper wire was invented? Two Jews fighting over a penny. And so on."
BBC Parliament is tagged as one of his favourite channels on Sky: he voted for "the gay policeman" (Brian Paddick) in the London mayoral elections and for Arthur Scargill in the European elections. He could never bring himself to vote Tory, but says, a little forlornly, that "the posh boys" he went to school with will soon be running the country. Without the cronyism and expenses fiddling of the last lot, he hopes: "I have a lot of faith in my generation. I have to. We have to develop our own moral system."
And finally, Radcliffe admits that as a boy actor he's had some "quite sexy mums over the years. Jamie Lee Curtis in [big screen debut] The Tailor Of Panama and Emilia Fox [in David Copperfield]. Both good," he says eagerly. He asks if I've met Rowling. "She is fantastically attractive. Very, very beautiful. And so intelligent, it's frightening."
Now, with the hour ticking on, the boy wizard must disappear. He has a 6am pick-up for a 7am start. It's just another day on the Harry Potter set - the Obamas are visiting.