"I love that scene!" he says. "It was so totally clumsy." He is delighted to hear that it made me laugh out loud. "Did you? Good. It's so totally malcoordinated when she asks him to kiss her neck and play with her at the same time. It's that first time experience when you're like, 'OK. What's this hand doing? What's that hand doing?' Trying to coordinate all those things at once the first time is an absolute nightmare. What I quite liked about that scene was that it's not sexy. It's a sex scene that's not sexy. It's clumsy and sweet."

And yes, he did touch the actress's breast. Wasn't it a bit weird? He gives an uncharacteristically teenage, duh-like "Nooo!" But contrary to his adolescent expectations, it wasn't at all sexy. "Kissing someone on camera is just not sexy, no matter how attracted to them you are. And Teresa is beautiful, so I was ... I was sort of worried about ... you know," - he lowers his voice slightly - "certain things. But it was OK. No matter how beautiful they are, when you're surrounded by crew who are taking measurements on the focus and making sure you're in the right light, it becomes totally clinical. And clinical is not a word I would associate with any good sexual experience."

"The first question I was asked on Equus was did I inhale, because there's a smoking scene in that," he says. "And I said, 'Well, yes, because if you don't inhale then you blow out about a ton more smoke than you would if you did.'" He found the fuss wearisome and ridiculous, especially given that his character did something genuinely shocking: blinding six horses. "But the RSPCA wasn't up in arms about that. It was a very bizarre, double-standards thing which sort of frustrates me.

"To me, the thought that stuff might upset Harry Potter fans didn't really come into it, because the reason I act is first and foremost for myself because I enjoy it, and second to serve the script. So if the script says smoke, I smoke. If the script says have sex, I have sex. So that's just what you do as an actor."

The teenager had just disrobed for his final sex scene in the play in June (07) when the girl dashed towards the Gielgud Theatre stage and grabbed the shorts her hero had just removed. He recalls, "They were just lying at one corner of the stage. I think she actually got them and started to leg it off and somebody had to chase her and get them back."

"The thing I keep having to remind myself about is this was designed by John Napier, who designed the original; it’s directed by Thea Sharrock, who will end up being one of the most important directors in British theater. And I’m with Richard Griffiths, who has more experience than anyone. So if I’m going to screw up, I could not screw up with better people around me.”