Something like this was bound to happen. They started off as innocent little kids but, as they got older, certain urges were always going to bubble to the surface. Now everyone's at it, as Hogwarts has turned into a veritable snogfest.

Kiss-a-thon: Rupert Grint and Daniel Radcliffe

All of the main characters are playing tonsil quiddich - Harry and Ginny, Hermione and Ron. But, in real life, we're told it was more like hard work than unbridled passion.

At last night's premiere of Harry Potter And The Half-Blood Prince in Leicester Square - which was wetter than the most slobbering of smooches - the stars revealed there was a lot more going on behind those on-screen smackers. Harry Potter himself Daniel Radcliffe told us about his on-screen snog with Ginny Weasley, played by young actress Bonnie Wright. He said: "My kiss with Ginny was a lot more gentle but still passionate, it took two days to film.

There is no way you can practise these things so we spent two days rehearsing and then just went for it, it was an amazing experience."

Bonnie seemed to think the experience was just as "amazing", saying: "It was tender and romantic. Dan's a good kisser - he's the hero of the film." But when pushed to comment on the experience with Daniel, rather than his on-screen character Harry, Bonnie would only say: "I can't judge it in that way, it was just acting."

At least Daniel and Bonnie sounded like they had a better time than Emma Watson and Rupert Grint - the long-anticipated kiss between Hermione Granger and Ron Weasley sounded like a positively awful experience.

Emma told us she had recently shot the scene with Rupert for the final Deathly Hallows film.

Speaking about their on-screen chemistry, Emma said: "On screen kisses are never nice and you sort of dread them. We know each other so well we are like brother and sister, and everyone on set was teasing us about the day we would have to kiss. But actually Rupert's a real gentleman and if I had to kiss anyone I'm glad it was him. There were no tongues involved."

Rupert added: "I filmed the kiss with Emma on the next movie a couple of weeks ago, it was weird. We've known each other so long and neither of us really wanted to do it but we just had get on with it, get into the character and then is was quite nice, but we were in a scary place to begin with."