Watching movie royalty such as Johnny Depp and Helena Bonham Carter belting out show tunes is a curious sight, one that is central to the allure of Tim Burton’s macabre Broadway adaptation Sweeney Todd: The Demon Barber of Fleet Street. Here Depp plays the titular barber who avenges the loss of his beloved wife with cutthroat razors and natty lyrics. Yet the movie’s real stars are the four young musical dynamos and hipster song-slingers who surround Depp and co with pitch perfect delivery, bathe them in flawless harmonies, match them with on-camera smarts and, well, ultimately make the Alist look good. Here are the four Sweeney showstoppers coming soon to a multiplex near you.

Jayne Wisener

It started with West Side Story. In 2006, the 20-year-old novice was spotted by a Sweeney Toddcasting spy singing the track Somewhere(lyrics by Sweeney’s Stephen Sondheim) in the Millennium Forum in Londonderry, in her native Northern Ireland. The next day she was told to record herself speaking and singing in an English accent. The tape was hurried to Sweeney HQ, where the hunt was on to find the perfect Johanna (corseted captive of Alan Rickman’s Judge Turpin, and love interest of Campbell Bower’s Anthony). And the rest, well, “I can’t believe that two years later I’m sitting here doing an interview for my first movie,” she says, bemused by her rise from local teen theatre wannabe to movie starlet.

The journey from stage to screen hasn’t been without hiccups. A boozy cast Christmas party on the night before a personal audience with Sondheim was not a good idea. And the technical realities of screen acting had their own challenges. “I was way too loud. I could barely hear Alan Rickman, who was speaking so quietly. I was like, ‘Doesn’t he know about projecting your voice?’ But I was reminded that it was film, and I didn’t need to shout.” Her startling performance has already snagged her a place in the Tony-winning musical Parade(at the Donmar Warehouse), and she’s currently planning her next screen appearance. In the meantime, she’s trying to adjust to the rarefied air around her. “I’m still reeling from the London premiere,” she says. “I don’t think I’ll ever look at Leicester Square the same way again.”

Ed Sanders

There are few actors who would attempt to steal scenes from both Sacha Baron Cohen and Johnny Depp, but Ed Sanders gives it his best shot. As a London street urchin in a blond fright-wig, the 14-year-old Forest Row native takes chunks out of Sweeney’s headlining cast and dominates entirely his spiky introduction, as a beleaguered assistant to Baron Cohen’s sinister mountebank Aldolfo Pirelli. That scene, a complex musical number filmed in front of 300 extras, was relatively easy, he says. The hair, however, was another story. “I think that the wig was meant to look quite ridiculous,” he says, unimpressed. “They succeeded in that. But I wasn’t very happy.” Sanders, a musical prodigy who’s been playing the guitar since he was four and is in three rock bands, is unable to watch his movie in the UK, thanks to an 18 certificate for graphic violence – Sweeney’s quest for revenge is accompanied by, literally, geysers of gore. “But when you’ve seen how they do it, it’s hilarious,” he says. “You have people pumping blood through tubes connected to the victim’s neck. Tim [Burton, director] even came on with a bucket and a syringe and was squirting it everywhere.” For now Sanders says that he’s craving school, family and normality, though he wouldn’t sniff at a movie career, as long as it was musical. “I can’t separate music and acting,” he says. “They’re both dream professions.”

Jamie Campbell Bower

“You have Johnny Depp, Alan Rickman and Timothy Spall, all with dark, interesting characters. Then I come along and it’s, ‘Oh just f*** off! We wanna see Johnny do his thing!’ ” Jamie Campbell Bower is describing the perils of playing Anthony, the love-struck sailor and sweet-centred heart of Sweeney’s nightmarish world. Yet somehow the 19-year-old’s screen charisma, subtle command and fey, otherworldly looks have transformed the role into a calling card for an increasingly hot player – he’s just finished shooting Guy Ritchie’s latest gangster flick, RocknRolla, and, 48 hours after our interview, he flies to Denmark to meet Lars Von Trier about a new project. Plus, internet rumours of a coveted place in the next Harry Potter movie abound. Campbell Bower was an A-level pupil at Bedales School in Hampshire when a family friend suggested he audition for the role of Anthony. He has since abandoned his studies in favour of the limelight and seems to be coping with his newfound status. He adds that he’s still working in a shop, an interior design store in Notting Hill Gate, and is quite prepared to let go of the Hollywood dream. “I could end up going, ‘I used to be that guy in Sweeney Todd!’ And I’m willing and ready for that, if it happens.”

Laura Michelle Kelly

Kelly is clearly the heavy-hitter of the bunch. The 26-year-old musical veteran arrived on set boasting lead roles in the London stage smashes Mary Pop-pins and Lord of the Rings as well as Broadway’s Fiddler on the Roof, and a recently released album of self-penned songs and covers called There Was a Time (produced by the Rufus Wainwright collaborator Marius de Vries). And yet playing a role that mostly required her to appear as a scrofulous beggar-woman wasn’t easy. “People didn’t know how to relate to me on set,” she says. “I was covered in sores and snot, and they just shied away. Luckily, Johnny put me at ease by kissing me on the cheek when I was at my ugliest.” The Isle of Wight native, who’s been acting professionally since she was 11, next plays opposite Kevin Spacey and Jeff Goldblum in the West End theatre production of David Mamet’s Hollywood satire Speed the Plow. Her Sweeney experience, she says, has been life changing, despite the fact that her considerable va-va-voom was hidden under layers of repellent make-up. “I get to be pretty and dress up a lot of the time,” she says philosophically. “If I want a career as an actress I want to be seen as a versatile woman. And besides I can’t do the pretty thing for ever. It’s too much to live up to.”

Sweeney Todd is released nationwide on Friday; director Tim Burton is the subject of The South Bank Show on Sun; see page 41

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