Helena Bonham Carter has been enamoured of Stephen Sondheim's musical 'Sweeney Todd' since she was a teenager. So when the part of Mrs. Lovett, who helps the revenge-bent barber set his murderous plan in motion, became available in Tim Burton's big screen adapatation, she jumped at the chance…

"I remember sitting in my drawing room looking at the score, going through the lyrics and listening to it," Bonham Carter says. "I got completely hooked on the music. I’ve always loved Sondheim. He’s such a genius to be able to write both lyrics and music."

But her love extended further than just an admiration for Sondheim’s music and lyrics. "I wanted to be Mrs. Lovett since I was thirteen," she laughs, "and I went around, apparently, in Mrs. Lovett hairdos."

But Bonham Carter didn’t know if she could really sing the role. "I've always wanted to be in a musical but I never thought I could sing, except in the bathroom," she says. And so Bonham Carter gave herself three months to learn. "I went to this amazing teacher named Ian Adam," she explains.

"He died recently, but he was quite famous for making actors who can't necessarily sing, singers too. Ninety percent of what he does is give you confidence and a self-belief that makes you able to open your mouth and produce a sound. From June to September of 2006, I sang every single day and I learned pretty much the whole score because I was very, very keen."

Although Bonham Carter had worked with Burton on 'Planet of the Apes' and later 'Big Fish' and 'Charlie and the Chocolate Factory', the idea of casting her as Mrs. Lovett brought a unique set of complications, not the least being the perception he was giving her the part because she was his girlfriend.

"I was very nervous about it, because it’s a big role. And it wasn’t just me. It was Sondheim who had to okay it," he reflects. "With a role like this, you’ve got to be able to really, really deliver."

Without knowing Burton’s choice, Sondheim watched all the candidates’ audition tapes and also opted for Bonham Carter.

"That was probably the best day of my professional life to be absolutely honest," Bonham Carter recalls. "I was in complete shock and, to be honest, Tim was, too."

"She’s very brave," says Johnny Depp, who plays the title role. "I mean, without question, that’s the toughest part in the movie and she beautifully made it her own. She made Mrs. Lovett kind of vulnerable and horrific and funny and sweet. There’s a lot of angles on that woman that Helena brought to her."

"I saw her as totally amoral, full of zest and full of life, and a survivor," says Bonham Carter. "Somebody who was as zestful and vital as Sweeney, was depressive and introverted, and very canny and a wannabe middle-class person. But the main thing that motors her, and the main thing that defines Mrs. Lovett is that she’s tragically in love with somebody who doesn’t love her back."

Q: So, was a musical something you’d always had on your list of to do?

Helena Bonham Carter: Oh, yeah but I’d sort of long given up on that. I thought it was always going to be a dream unfulfilled, so when this came around, I thought: 'Well, I can’t not go up for this. I can’t let this one go by particularly since not only have I always wanted to be in a musical, and at least get the chance to sing that I’d love some time, and I’ve loved 'Sweeney Todd' since I was really, really small, 13, and I’ve loved everything that was written.'

So, I just you know, I couldn’t not try. I pushed every ounce in my little enlarged being. It was truly an act of determination because I hadn’t sung before, and I had no idea how to do it, but I just thought I had to try, with every bit of me, and I only just wanted the intensity to do it. I had to audition because anyone who wants to play this part is going to have to audition. And Stephen Sondheim’s going to have casting approval, but please try out. And so, I’d been practicing pretty much nonstop. And when I got the part, then I go: 'Oh my God, now I really have to learn the rest of it.'

Is there a song that you’re particularly proud of?

To be honest, I’m proud that I did it, put it that way. I’m proud that I did a few. For me to sing in front of Stephen Sondheim, that was a big one. Just a dream. It was like me winning 'American Idol', I couldn’t believe it.

As a fan of the musical beforehand, what is it about the songs that resonate with you?

I just love all of his music. There’s a romantic yearning. Actually, it’s the men’s songs, to be honest. Mrs. Lovett doesn’t have pretty ones. She has the difficult ones. But ‘Pretty Women’ and ‘Joanna,’ they’re so soulful and beautiful. They’re a bit of blend of heart and soul but also real wit and ingenious lyrics. To be able to write the music and the lyrics and then working on it, you just think he’s even more of a genius because I listened to orchestration, when you’re given this bit to sing along to, and without your melody, there’s so much going on when you hear everything else, so many layers of all these different instruments and somehow it harmonises all into this amazing thing.

Did you think the songs stand alone, or do you think they go best with the story?

Oh, no, they stand alone. People know 'Nothing’s Going to Harm You'. I used to sing it to [my son] Billy. It’s like a standalone lullaby, my lullaby that I sang to Billy for years. ‘Joanna’ is like a soul song and ‘Pretty Women’. There are some great tunes you can’t not be singing along to, and the crew, who didn’t know Sondheim, everyone’s singing along or humming along. And, also, I think the way Johnny and Tim saw the takes, not so much with the way I do them, but Johnny’s voice has a much more modern feeling to it. It’s not Broadway. And in fact, we were all taught, told to sing not in a very indulgent way. We like to stretch the words, but not to emote it. Just very simple, almost the same stress, as if we’re talking it, which is actually quite hard to do.

How do you find your voice for this, because obviously you recorded the music first? Did that influence your dramatic performance?

Oh, God, yeah. You had to do it all, in fact. You had to do your homework before they recorded because that’s where you’re going to commit to lots of choices. And then you got handed the finished song by the music producers, who’ve been working day and night putting all the different takes together. You then have to then go and learn that back to front because when it comes, you’ve got to know it.

The big thing I learned about this, which is great, was muscle memory. If you do something enough times, your body will know what it’s doing or your lips would know or your brain, and you don’t have to think about it. So, we listened to it, and you’re not sure what the rhythm is, it’s inside you. You swallow it, and it’s there. Then you get on the set, and you realise: ‘Oh, I mean little thing,’ logistics.

The physicality of getting from my pie place to the door to get Sweeney from the moment I see him — ‘Wait, what’s your rush? What’s your hurry?’ Everything, we had to literally rehearse and rehearse and rehearse, and [they] had to add a few bars, or take a few bars out because I couldn’t get to the door in time to be back at the counter for the first beat, when I start with the pie, which is written into the music. So, it’s fairly complex.