A romantic moment for Harry Potter ©2009 Warner Bros

There’s romance in the air on the set of Harry Potter and the Half-Blood Prince . Hormones are erupting in all corners of Hogwarts and the cast is facing up to the film’s potentially embarrassing romantic moments.

For Emma Watson , who plays Hermione, this ­involves a budding romance with Rupert Grint , who plays Ron.

“Ooh! I don’t know if it’s tough,” she smiles shortly before shooting her first ­intimate scene at Hertfordshire’s Leavesden Studios.

“Rupert’s a really laid-back guy and I quite like the ­romantic-comedy side of it. It’s awkward doing the love scenes – there’s no other way to put it – but it’s just part of the job!"

And Hermione and Ron are not the only ones at it. As the film’s director, David Yates, puts it, the latest instalment in the boy wizard ­series is all about “sex, drugs and rock’n’roll”.

Harry ( Daniel Radcliffe ) finds himself increasingly attracted to Ginny (Bonnie Wright) and they ­exchange covert glances across piled-up ­platters.

And there’s ­Lavender Brown (Jessie Cave), who sets her sights on Ron, leaving Hermione seething with resentment.

"I think I would have been more nervous if I’d stepped on to the film without knowing Daniel and done a romantic scene"

“Having to do these ­romantic scenes is nerve-wracking,” concedes Wright, “but I think I would have been more nervous if I’d stepped on to the film without knowing Daniel and done a romantic scene.”

Of course, Ron and ­Hermione’s relationship is one that ­finally ­blossoms in the series’ final instalment, Harry ­Potter and the Deathly Hallows. “That’s a bit weird,” smiles Grint. “We know that it’s happening in the next film, but I’ve tried not to think about it. It’s strange because Emma and I have known each other for nine years.”

That said, in between 2007’s The Order of the Phoenix and The Half-Blood Prince, the main cast have spread their professional wings and return to the franchise with much more confidence.

Radcliffe took to the stage with Equus, and also shot ­December Boys and ITV’s ­Kipling biopic My Boy Jack; while Watson voiced ­Princess Pea in animation The Tale of ­Despereaux and starred in BBC family blockbuster ­Ballet Shoes.

“It was nice to come back and talk to Dan and Rupert about the projects they had been working on,” says Watson, “and how ­different it was to work on stage and TV. It’s given us all more ­confidence because we were chosen so young for the ­Potter films. It was so good for me to do Ballet Shoes.”

The actress turned 19 shortly after finishing work on The Half-Blood Prince, and is beginning to enjoy some of the perks of fame.

“It’s amazing getting sent Chanel dresses,” she beams. “I’ve always loved them. I don’t have time to go out to buy any clothes for events so they lend me them. I also consider it a perk that I get to travel and work with the people I’ve worked with. What other job would have given me these chances?”

And is there anyone she still hopes to meet? “I’ve never met Natalie ­Portman but my driver on the ­Potter films, ­Nigel, has driven her, so I’ve sat in the same car! I also met Johnny Depp during the filming for Charlie and the ­Chocolate Factory in Shepperton.” She stops and smiles. “And I’m still intimidated by ­meeting Jo Rowling.”