Harry Potter and the Half-Blood Prince is the sixth Harry Potter film. Do you think that there will be mixed emotions when you finish shooting the next films?
DANIEL RADCLIFFE: Definitely. It will be very, very odd to suddenly not be coming back to Harry Potter. It does act as a safety net, in a way, when you're going off to make something else. Knowing that you don't have that will be sad. I'll be sad to leave the character behind and not see the friends I've made on a daily basis.

The Harry Potter film series has been such an enormous part of your life. Do you ever look back over early films in the series and see how you have developed?
DANIEL RADCLIFFE: There's a certain amount of cringe in my own performance; so I don't look back on the early films. I probably should watch them and take the positives from the way my performances have improved and developed over the years but it's a little embarrassing to see yourself and hear yourself at that age. When I eventually do look back it will be very interesting.

Rupert tells us you're improving at the games of table tennis that you play when you are relaxing between scenes on Harry Potter and the Half-Blood Prince, but he says that Emma really knocks everyone else out?
DANIEL RADCLIFFE: Yes, and it's really irritating that Emma is so good! [Laughs.] Rupert and I had been playing for about eight months and working on each other's game. Then Emma saunters in and is absolutely brilliant. Neither of us could beat her. I have got better but I'm never going to take Emma on again.

Back to the world of Harry Potter. Will Harry Potter and the Half-Blood Prince show another side of Harry?
DANIEL RADCLIFFE: There's friction in this film it's much more to do with Ron and Hermione than it is to do with Harry. Harry is unhappy for a lot of this film, mainly because people keep trying to kill him. And his love life is awful, too. That's what Jo [JK Rowling] does so well: combining everyday, mundane problems with this incredible other world.

Were you happy to be back on the Harry Potter film set for Harry Potter and the Half-Blood Prince?
EMMA WATSON: I was quite keen to get back into the swing of it. Everyone was pleased to see me because it meant that things had really picked up.

How tough was it to have your character start a romance onscreen with Ron, especially since he’s played by an old friend?
EMMA WATSON: I don't know that it's tough. Rupert's a really laid back guy but I'm really looking forward to it because I quite like the romantic comedy side of it. Rupert and I end up providing light relief, as the films get darker. It's funny seeing Rupert struggling in the romantic stakes. Hermione and [Ron] are so different yet they have this chemistry, so it's interesting. It'll be awkward doing those love scenes; there's no other way to put it, but its all part of the job.

You are in great shape but are you naturally athletic?
RUPERT GRINT: Not really. The only sport I do is a bit of golf, really. Apart from that, I'm lazy so I've had to do a bit of training.

Do you think that you ever get used to all the attention that comes with the phenomenal success of the films?
RUPERT GRINT: I've gradually got used to it over the years. It's more apparent when the films come out. It's strange when people come up to you. People are always really nice though. It's never really gangs of people; it's usually one or two who come over. I don't mind that at all. Once, I was in TGI Friday and a guy with a camera happened to be there. That was the only time I had any paparazzi, as such.

Do you ever get called Ron?
RUPERT GRINT: People always call me Ron, especially the younger kids. My little cousins actually think I'm magic.

Was there ever any remote chance that you wouldn't come back for this sixth Harry Potter film?
RUPERT GRINT: For me, there was no doubt. So long as they wanted me, I was coming back to do it. I really enjoy doing this and it's really cool.

What’s it like coming back to work on your second Harry Potter film?
DAVID YATES: It’s lovely; it feels like home. There’s a tremendous atmosphere here and it’s very relaxed. We’ve got some lovely people. It just feels like being at home, really.

Do you feel more relaxed or more terrified because you know what to expect?
DAVID YATES: It’s kind of a bit of both. I felt really self-conscious making the last film. I didn’t realise how big it was until I got to the premiere and then got to America and saw how massive the release was and how huge the reaction was. That was when the penny dropped that this was such a big thing for so many people. Oddly, when I started this one, I was a little bit more wary of everything. The first time round you just do it; you just go for it. But I’ve settled in and this one’s quite different to the last one. It’s a little bit more grown up and a bit wittier. It’s a different vibe, I think.

Producer David Barron says it’s the fact that you’ve got the energy of a four-year-old that keeps you going.
DAVID YATES: And I eat a lot of profiteroles too. [Laughs.] Anything I’ve made before usually leaves me quite shredded, but there’s something about this and working with the kids – although they’re not kids anymore – that keeps me energised. I just really enjoy it. I enjoy it more than anything else, probably because it’s quite playful. Also, you get a tremendous amount of resource and time and I’ve got a great team. I have more time to shoot than I ever need, really, so it’s much less exhausting to shoot than anything I’ve ever done. Also, I come from television where you shoot 5- or 6-day weeks and shoot five minutes a day. Then you come to this environment and you’re shooting a minute a day or 30 seconds a day. So, it’s much less tiring.

How quickly did you decide to return and direct Harry Potter and the Half-Blood Prince?
DAVID YATES: I was in post-production. We were just finishing off Harry Potter and the Order of the Phoenix and we’d shown it to the studio and were just taking it to Chicago to test it with an audience. They asked me and I’d already felt that I wanted to continue. So, it was a good three or four months before the film was released.

Shouldn’t that be the time when you want to run away from it all?
DAVID YATES: Funnily enough, it was about halfway through making the previous one that I thought, I’m only going to do one of these, this is crazy. But I got a second wind and really loved the last few months and the post-production. And everyone’s just delightful to work with.

How would you describe this movie?
DAVID YATES: It’s love, potions and rock ‘n’ roll. There are all these wonderful things in our story. There’s a potion that gives you perfect luck. You take it and everything goes right for you. But it does heighten your senses somewhat and you get quite breezy with it. Then there’s a love potion that makes you very tactile with everybody. Rupert gets overly tactile with Jim Broadbent at one point. So, it’s got all those metaphorical values. There are some really lovely comic beats here, which we didn’t really get a chance to do last time. It was just a very different beast.

Are you conscious of a time when all the films will be watched back to back, so you have to keep a through-line?
DAVID YATES: Yes, and there is a through-line. We’re just putting in all sorts of little details between the characters, which hopefully will resonate through the films. There’s a line that goes right the way through to the end.