In my job I've learned to be rather blasé about meeting celebrities, but attending the Revenge of the Sith press conference on Tuesday morning, May 17th, at the Dorchester was different. Because George Lucas was going to be there. But we start with the three actors: Christensen, Daniels and Ian McDiarmid, who plays the chancellor/emperor Palpatine, aka the villainous Darth Sidious.

Daniels seems strangely subdued this morning--chatty but not quite as exuberant as the last time I saw him. Perhaps he was exhausted by the rigours of the world premiere at Cannes on Sunday, then the London premiere on Monday. Or maybe it's because he's sitting between Christensen and McDiarmid. Compared to them, Daniels seems like a wispy court jester--slight and smiley to Christensen's tall thespian swagger and jutting jawline and McDiarmid's forcefully Shakespearean air. All three speak with the clipped answers and pithy turn of phrase that comes with doing far too many press conferences.

But we have to start with Daniels, who is the only actor to have speaking roles in all six films. We're wondering when he realised this thing was so big.

'It was actually the cover of Newsweek magazine that blasted the whole thing - saying, "This is the best thing ever!" Star Wars opened with no publicity, it was just audiences going in and coming out screaming, and taking their friends in, and so it built,' he says. 'But originally Star Wars for me was a 12-week gig and that was it. It's 30 years since I met George in an office down the road from here. I didn't want to meet him. I didn't want to play a robot in a low-budget sci-fi movie. Can you imagine how I would have felt today being a shelf stacker in a supermarket going. "I could have been in that movie!" So I guess the Force was with me.'

McDiarmid starred in four of the films (and Lucas added him into Episode V for the 1997 Special Edition). He gets to be the villain of the piece, even more fearsome than Darth Vader. 'It's interesting, especially in the prequels because, for those who didn't see Return of the Jedi, I just play a straightforward politician. Now there's a contradiction in terms - charming, smiling, out for the good of the world and the universe. But underneath that there lurks a monster. So it was very easy to build a character,' he says, pausing for a comic beat. 'I just looked in the newspapers' - then takes a well-timed sip of water.

Of course, the make-up helps with the transformation. 'It always helps,' he says. 'It certainly helps to be a monster in monstrous make up. But George was very interesting when we started The Phantom Menace. He said I should think of my eyes as his contact lenses, which was a great thing to say to an actor. So my face was actually his mask, and when I put on the mask I become him. So that kind of schizophrenia was always fun to play, and in this film it's great because one explodes through the other, and now he is who he is: worse than the devil. And certainly worse than Darth Vader, who I think comes across in this movie as more sympathetic than people might imagine.'

And now to Christensen, the newcomer with only two films under his belt (plus a digital cameo added to Episode VI for the DVD release). Was it painful to undergo the transformation from bright young Jedi to gruesomely deformed Sith Lord? 'The pain and suffering actually came when they took the prosthetic off,' he says. 'They made this full-body prosthetic, which they would glue to every inch of your face. Putting it on was fine; taking it off was a different story. It was full-on make-up that, looking at yourself in the mirror, made you react to it, which was nice. Being unrecognisable obviously aids in making that transformation. But it was a thrilling moment lying on the operating table as that mask came into frame. It was good fun.'

And people were taken aback when he strode onto the set for the first time in the Vader suit. 'They reacted,' he says with a smirk. 'That was what was thrilling about getting to put it all on and experience the sensation of being Vader. But watching everyone take him in for the first time was really cool. People that I befriended and spent a lot of time with, who knew I was in the costume, would see him and, while there was an excitement and a certain awe, there was a fear and a respect that needed to be paid. So as I would walk by their eyes would light up and then they would lower their heads a bit and take a couple of steps back. It's a very empowering feeling.'

Clearly he relished filming those final scenes in the full regalia. 'Oh yeah, it was Vader's day and it was the last day of filming as well,' he smiles. 'Everyone from the production offices and everyone working on the film came out to bear witness. It was an exciting day. Obviously in this film getting to become Darth Vader and put on the costume, and have that card in my back pocket now, was the best bit.'

So what was the best bit for McDiarmid? It had to be playing the villain of the piece, he says. 'Yes. he is the darkest of the dark, the blackest of the black, worse than Satan. It's fun! You're not going to get a part like that every day. I like the fact that he doesn't really have any psychological workings. He was spawned in Hell in a way. Siths are, apparently. They can't get better. Except as you see in the movie he goes to the opera, so his one redeemable feature is that he's a patron of the arts." He smiles knowingly and takes another expertly gauged sip.

Certainly, after six films Daniels has a lot of best bits. Although he doesn't have many nice things to say about the Threepio suit. 'The costume was made to a mould of my body, and in the manufacturing it all shrank,' he says, casting his memory back nearly 30 years. 'On the first day it took two hours with six props guys squeezing me and pushing me in there. My moment of joy came finally stepping out of the tent in the desert and seeing the whole crew - American, English and Tunisian helpers. The Americans would go, "Gosh, that's incredible!" The English would go, "That's quite interesting, isn't it?" And the Tunisians would fall to their knees thinking I really was the second coming. That was my moment of joy. The next moment the assistant director asked if I could come over to the set, and I took one step in the costume and it broke and nearly cut my foot off. I knew I was in deep doo-doo from then on.'

Over the next 30 years he had to keep his weight down just to fit into the thing. 'If you've met [producer] Rick McCallum, you know they're not about to make a new costume every time we do this thing, so I'm actually wearing the same costume. It's beginning to smell a bit now. Like Hayden, I work out a bit to stay strong and stay healthy.' Although he didn't get a bare-chested beefcake scene like Hayden does in Sith.

Ewan McGregor has gone on record that making Star Wars movies is very difficult for an actor, what with all the green screens and empty sets filled in later with special effects. But surely one of Christensen's biggest challenges was keeping a straight face opposite Natalie Portman's elaborate hair-dos. he laughs, 'There was a new hairstyle every day, more elaborate than the next. Good for her, she can pull them all off which is pretty impressive.'

Daniels' main challenge was to carry on conversations with bleeping sidekick R2-D2 (Kenny Baker). He found it rather difficult to talk to himself through most of the movies 'Artoo is adorable, but he doesn't speak,' he says. 'It's kind of hard to do a performance with actors who actually don't respond. I tried to get George to go "beep" at the end of a line I'd said. I was explaining how difficult it was and asked if he could do this. We were out in the desert and he said, [cue the dead-on Lucas impersonation] "Oh, sure." So we did the scene again and he went, "Beep". But from then on it was up to the sound guys.'

Acting wasn't always Christensen's goal in life. 'I fell into it actually. I grew up playing sports and, though I acted from a young age, it was more a hobby than anything else. I studied it in high school and that's where I felt my passion for it.'