Leonardo DiCaprio’s face, half in shadow, looms large over us all. The lit match between the fingers of his left hand is his only weapon against the encroaching darkness. Well OK, it is not actually the actor himself (he has yet to arrive) but a cardboard effigy cast in his image to promote the new film Shutter Island. There is little chance of blackness engulfing those assembled for the movie’s press conference here at the Dorchester Hotel. The vast room we are in is bright and dominated by a crystal chandelier which hangs over our heads.

The marketing image, which will soon be seen on billboards and buses across the country, has been well chosen as it is an encapsulation of the themes of Shutter Island. In this gothic thriller DiCaprio plays U.S. Marshal Teddy Daniels who is charged with investigating the mysterious disappearance of an inmate from a high security mental hospital located on the titular isle. Daniels is suffering from PTSD after taking part in the liberation of a WWII concentration camp and uncovers not just the secrets behind the island but also terrible truths about his own past. The plot, based on a novel by Dennis Lehane, is multi-layered, labyrinthine and pretty darn bleak.

By the time the film is over the storyline has encompassed murder, government conspiracies, anti-commie super soldiers, Nazi scientists and Lord knows what else. The fog that surrounds Shutter Island throughout extends to the audience’s perception of events and even as the credits roll there still remains the possibility that they have been hoodwinked. Perhaps a meeting with Mr. DiCaprio, his co-star Sir Ben Kingsley and the film’s director Martin Scorsese will help sort things out.

The trio of big names have only just flown in from Rome and DiCaprio in particular is subsequently both tired and tanned. I can empathise having just taken the tube in from Ealing that morning. All three men are expensively suited although only Scorsese has deemed to wear a tie. In the brief time that we are granted they are treated with respect and reverence. There are no novelty questions asked or private lives probed as today’s crowd, to the delight of the star guests, just want to talk about movies.

Firstly, DiCaprio is quizzed about the demands of a role in which he appears to go through hell. Shutter Island sees him battered by wind and rain as well as at least one of the hospital’s inmates, swim across freezing water and even walk over a carpet of live rats. Not to mention the psychological trauma that his character is subjected to. Was all this, as one wag suggests, an atonement for his privileged lifestyle?

DiCaprio laughs before explaining, “It was the nature of the material. Throughout the course of the movie you learn different aspects of Teddy’s past and it’s a traumatic truth. To make the set of circumstances believable we had to push the emotional extremes, taking Teddy to darker and darker places. Some of the sequences in this movie really shocked us.”

With the hardships the actor experienced, did he feel it difficult to switch off at the end of the day? “This is perhaps the most challenging role to date for me,” he responds, “physically, yes, but emotionally more so. In order to survive the film making process I do switch off because if I don’t…” DiCaprio stops mid sentence and we are left to contemplate the worst.

DiCaprio reveals that he did have a way of coping with working on a film which paints a less than rosy portrait of human nature as well asking some difficult moral questions. “I do like to isolate myself from other people when I am filming for months at a time,” he says. “There was a sombre mood on this movie. You are feeling emotionally vulnerable and you need someone there to guide you. I am glad I did this film with Marty.”

Ah yes, Martin Scorsese who, upon arrival at the conference table, spends a while staring down at his feet in a self-conscious manner. Perhaps the shy, sickly New York kid who developed an absolute passion for the moving image and grew up to be one of it’s greatest practitioners stills feels strange to be the centre of so much attention.

When you ask Scorsese about cinema it is just a case of lighting the blue touch paper and stepping back. He rattles off the reference points he used for Shutter Island, from the works of Sam Fuller and John Huston to Otto Preminger’s noir masterpiece ‘Laura’ which he cites as the most profound influence upon his film. When he speaks of his treasured 35mm Technicolor print of Vertigo it feels hard to imagine that any human being has been the subject of such intense love.

Scorsese’s knowledge of film is famously vast (Tarantino is just winging it in comparison) and this is highly evident in the look and feel of Shutter Island. “The first element I connected with was the emotion” Scorsese says of his new baby, in his familiar jackhammer delivery. “That and the vocabulary of the past of cinema and the nature of gothic literature. I don’t know how else how to tell the story but to utilise that vocabulary.” For a man who numbers Raging Bull, Taxi Driver and The Departed amongst his credits, Scorsese is remarkably modest. When asked how he feels about being labelled ‘the greatest living film director’ he jokingly interjects even before the questioner has completed his sentence. “I didn’t say that!” the director protests, “I didn’t say that!”

“All I can do is the best work I can. I need to work, I like to work-although I complain about it - and I just can’t think about it. It would be nice if the film is recognised in the awards period but it’s just a battle to get through the film and make something I can be happy with. Sometimes you go in with one thought in mind and by the second or third week you just want to survive it.” He is eager to stress that though his films may begin as his concept they soon become a collaborative effort involving his regular team, all of whom are essential to the creative process. They include, “Bob Richardson on camera, Dante Ferretti on production design… and ultimately Thelma Schoonmaker who keeps me focussed in the editing of the picture.”

Since Gangs of New York, their first film together in 2002, through to The Aviator and The Departed, DiCaprio has obviously become a trusted part of ‘Team Scorsese.’ The torch has been passed on by Robert DeNiro, making Leo the go-to guy for Scorsese’s above the title roles. In doing so he has benefited from greater kudos as an actor, overcoming his baby-faced looks (he is as handsome off screen as on, damn him) and maturing into a believable leading man. When it comes to the meaning behind the film’s ending however, he is giving nothing away.

“We were very conscious that we were doing a movie that would have a different interpretation the second time around,” says DiCaprio. “ There is a certain level of ambiguity at the end of the movie and throughout which could lend an audience to have a different experience on further viewings.”