Baritone William Shimell had a whirlwind May.  Deep in rehearsal for Covent Garden’s new production of Manon, he was whisked away for a crazy 48 hours in Cannes to promote Certified Copy, the movie he made last year with French star Juliette Binoche and film director Abbas Kiarostami.

Summer in Tuscany in the company of one of the world’s most beautiful actresses; it must have been a tough assignment, I suggest when I meet the singer turned actor at the Royal Opera House a week before the Massenet opens.  “It was actually a bit of a nightmare,” he laughs, not because his star and director were ever anything less than wholly supportive but because he felt “completely thrown in the deep end.”

Shimell had first worked with the Iranian director a year previously at Aix-en-Provence, where he’d played Don Alfonso in Kiarostami’s debut opera production of Cosi fan tutte.  A seemingly chance comment (“Do you want to be in a movie?”) unexpectedly turned into the real thing and he found himself co-starring with an Oscar winner in the director’s first European feature. “It was not something I could prepare for,” says Shimell, “because it’s something I had absolutely no experience of.”

The film is an elliptical love story, with Shimmel as a writer who Binoche picks up at a presentation.  It’s unclear whether they know each other and the story unwinds in an unconventional narrative.  “It’s difficult to describe the plot,” he says, “everyone sees something different in it.”

“ The first scene we shot was the first scene you see in the film.  Me presenting my book to an audience.  So, there I was in front of a whole lot of extras doing a six minute speech.  It was so stressful I just had to blank it all out and had to just concentrate on the work.  There was no room for fear though that’s what I was feeling.”

“I learned the script before we started,” he says, “which is quite unusual in films but I didn’t have a lot else to go on.  And then of course, after a day it all changes anyway.  So, it was a case of learning quickly.”

I ask him how he coped with the Cannes circus last month.  “It was quite extraordinary,” he says, “it’s something you have to do once. I took a job, turned up and did it but didn’t quite realise the significance of it all.  Then you go to Cannes and you’re in the company of one of the world’s finest directors and Juliette who’s a mega-star and ME!  I mean, come on.  Suddenly you’re the focus of all this attention.”

“Cannes is there to sell films and it’s a huge barrage of publicity.  It’s all about selling the product.  Many actors would give a limb to go to Cannes and there I was just by accident.  I felt something of a fraud.”

Although he has 30 years of experience as an opera singer Shimell has never appeared as a “straight” actor on stage, let alone in a major movie.  As any actor will tell you, it’s a completely different craft from stage acting and quite a leap the first time you do it.  For someone used to the less natural demands of opera acting, it was something else.  “30 years of opera experience was completely useless,” he tells me.

Mind you, Shimell is a performer who takes a naturalistic approach to his singing career producing portrayals of great subtlety, “sometimes too much so for some people,” he says.  I venture that the need for truthfulness is present as much on the opera stage as in front of a camera, if not to quite the same degree.

“I’ve always found opera performing somewhat limiting,” he says.  “The reason I like to sing the da Ponte operas so much is they allow you to be so real.  Night after night it can be completely different.  There’s such depth in the characters, unlike in a lot of other operas.  Transferring that to the film experience was one of the interesting things about it.  It was a different form of expression.  You can’t “act” at all.  The camera picks it up straightaway. ”

I ask him if it was true that Robert de Niro was rumoured to be in line for the part at one point.  “Thank god I didn’t hear that until after it was over,” he says, “that would have been a little too daunting.  Certainly a lot of actors were considered, including a couple of very famous French stars.  I suppose Abbas changed it to an English character once he’d settled on me.”

Binoche went on to win the Best Actress at Cannes, so Certified Copy is sure to get a fair bit of attention on its UK release.  Shimell has been a wickedly charming Don Giovanni for many years but clips of the film, which can be seen on Youtube, suggest that his brooding, under-stated performance will win him many new female fans when it’s seen here in the autumn.

Such is the life of a jobbing performer that Shimell has gone from film star back to the day job, playing the relatively small role of Bretigny in Laurent Pelly’s new production of Manon at the Royal Opera House.  “I think it’s going to be a big hit,” he says, “Anna Netrebko is going to be stunning.  She’s such an extraordinary talent. I worked with Pappano (the conductor) years ago here in La boheme and he’s great too.”

“I haven’t got a lot to do, so it’s a fairly easy evening for me.  Bretigny is a dirty old man. He sees Manon early on, when she’s just 16 and he basically buys her.  I can’t imagine why they’d cast me in a role like that!  It’s a big show with a big cast, needing a lot of resources.  I think people are going to really like it.”

Shimell has a schedule of operas lined-up which includes “some Cosi’s” and appearances at La Scala.  Before his recent Don Alfonso at Covent Garden, he hadn’t performed in London for some 13 years and, with nothing else on the horizon, audiences will have to get along to this month’s Massenet to catch him before Certified Copy gives him a whole new exposure.  At this stage of his career, I get the sense that Shimell wouldn’t be at all unhappy if, with one starring role under his belt, he got the call to get back in front of the camera.

Manon opens at the Royal Opera House on 22 June and plays for six performances.  Full details at www.roh.org.  Wiliam Shimell will play the role of Bretigny in the Royal Opera's tour to Japan in September.