Fairytale team: James Corden, Anna Kendrick and Rob Marshall talk Into the Woods

And not just any Hollywood makeover, but a Disney-backed one, helmed by blockbuster director Rob Marshall, whose previous credits include Pirates of the Caribbean: On Stranger Tides and the Oscar-winning adaptation of Chicago.

Marshall is a man with musicals in his blood – he started out as a Broadway dancer – and Into the Woods has been a longtime labour of love. It all started when, fresh from the success of Chicago in 2003, he approached Sondheim about adapting one of his musicals, and the composer suggested his fairytale fantasia.

Fast forward nearly ten years and Marshall was listening to President Obama address the families of the victims during the tenth anniversary commemorations of 9/11. In an effort to console them, Obama uttered the words "You are not alone… no one is alone," which, as any fan of Into the Woods will know, is pretty much a direct quote from the show.

This prompted Marshall to reimagine Into the Woods as, in his own words, "a fairytale for the 21st century post 9/11 generation," and the wheels of the film were finally set in motion.

Speaking to Marshall in a London hotel suite, I'm intrigued to know how he's handled the expectations that come when filming a musical beloved by so many people. "I like that people are passionate about the piece – I'm passionate about the piece, that's why I wanted to bring it to film," he enthuses. "And I want to remind everybody that James Lapine wrote the screenplay, and Stephen Sondheim worked with us on every bit of it."

Lapine and Sondheim, he says, were "incredibly flexible" to the necessary alterations, even writing a new song especially for the Witch, played by Meryl Streep (though it ended up on the cutting room floor and will now appear on the DVD extras).

"I think the biggest disservice you can do to a stage piece is to take it as it exists on stage and put it on film," adds Marshall, whose other credits include Nine and a made-for-TV version of Annie. "It doesn't work, we've seen that over and over again. It should work, but it doesn't, because they're completely different mediums."

He's keen to point out that every change – notably cutting the show by 45 minutes, with the second act becoming more of a denouement with a twist – was "meticulously" considered. And having seen the film, I can attest to the fact that it feels so true to the spirit of the stage show that, come the end, I was scratching my head to recall exactly what had been cut (and I speak as somebody who once appeared in a student production).

'Heartbeat of the film'

Casting Into the Woods was no small task, considering it's an ensemble piece with over 20 major characters. But Marshall has, well, marshalled a hugely impressive list of names, from the likes of the aforementioned Streep and Johnny Depp (as the deeply Freudian wolf) to stage stalwarts Simon Russell Beale and Frances de la Tour.

If it does have a central role, it's the Baker, whose mission to undo the Witch's curse on his fertility drives most of the narrative. It's an everyman role, and with this in mind Marshall turned to James Corden, well known to theatre audiences thanks to The History Boys and One Man, Two Guvnors, and about to become a lot more famous in America as the host of CBS's The Late Late Show.

Reclining on a sofa in a neighbouring hotel suite, Corden tells me that the key to the Baker is "restraint", about channeling the sense of a "regular guy caught up in irregular cicumstances".

"He's not very showy," says Corden, "though in the last ten minutes he really holds the heartbeat of the film."

Corden was cast after taking part in early workshops held by Marshall during the planning stages of the film. It was thanks entirely to Marshall's faith and insistence – in the face of more famous competition – that he ended up playing the role on screen. And his adulation for the director is clear, when he describes his filleting of the convoluted narrative as "miraculous".

Starring alongside Corden as the Baker's Wife is fellow Brit Emily Blunt, who's become a big Hollywood player thanks to films including The Devil Wears Prada, The Young Victoria and Looper.

Blunt, who's currently away promoting the film in China (an advantage of such a large cast is that they can do interviews in all corners of the globe simultaneously), gives "the performance of her career so far" in Into the Woods, says her on-screen husband.

"The first thing a lot of people say to me when they've seen the film is that my chemistry with Emily is great. And I wish I could say we've worked on it but it was just there, it just kind of happened."

It's no accident that they're both highly skilled comic actors, and this shines through in the film. When Corden tells me that recording their duet "It Takes Two" was "the best day of filming I've ever had," it comes as no surprise.

'Sondheim doesn't suffer fools'

Another cast member with an assured comic and musical touch is Anna Kendrick, she of 'cup song' fame and more latterly star of the film version of Jason Robert Brown's The Last Five Years.

She plays Cinderella, who in Sondheim and Lapine's retelling runs from the Prince (played by Chris Pine) on three consecutive nights. But, as with most of the characters in Into the Woods, their happy ever after doesn't last for long.

"I was desperate to do it," says Kendrick, whose background is in musical theatre. "And I feel very lucky to be working in a time when movie musicals are being produced, because they can be few and far between."

She credits Marshall's Chicago with the current boom, while the runaway success of Les Misérables in 2012 has no doubt given it extra fuel.

As for Cinderella, she disagrees with the suggestion that Sondheim and Lapine portray her as something of a manipulator: "The fact is that in her gut she feels there's something fundamentally wrong with the idea of running off with a man she's done nothing but dance with. I think as women we naturally don't trust our instincts and doubt ourselves. She's incredibly indecisive, and that has consequences, but it's not manipulative or intentional."

Kendrick's big number is "On the Steps of the Palace", sung whilst she is "stuck with a shoe/in a stew/in the goo" with the Prince just a few steps behind her. It's a scintillating performance that underlines Kendrick's status as Hollywood's leading young musical actress.

"The set [for the song] was all real, including Chris Pine who had to stand frozen still for two days. Rob [Marshall] creates such a heightened environment on set that it doesn't feel ridiculous to burst into song, it feels perfectly natural. He plays the music at full volume and he make sure there's nothing in your eyeline to distract you – to do that song against a green screen with a tiny earpiece would have been much more difficult."

It's a fascinating glimpse into the theatrical working process of Marshall, who is a Tony nominated director and choreographer. He clearly took a different approach to that of Tom Hooper's famously stripped-back techniques on Les Mis.

And how was Sondheim as a collaborator? She thinks carefully, before replying: "I really do enjoy people who intimidate you, because it's possible that they'll say something that might hurt your feelings. Sondheim is a guy who doesn't pull any punches or suffer fools, so to me it's so much more rewarding when he just says 'that looks good, let's move on'."

Kendrick's obvious awe for the composer strikes me as the key to this whole project, for it's clearly shared by all those involved. And for Sondheim's many aficionados, Into the Woods marks a landmark moment, a potential for him to find unprecedented mainstream success.

Time will tell whether his anachronistic composing style will prove a hit with a wide audience, and indeed how his dark twists on the stories of Cinderella, Jack and the Beanstalk and Little Red Riding Hood will play with a Disney demographic.

But one thing's for certain, with a company boasting the likes of Marshall, Corden and Kendrick, he's found as loyal a band of apostles as he could possibly hope for.

Into the Woods is released in UK cinemas on 9 January. Look out for our full interview with James Corden, which will be published over the Christmas period.