Leo gets behind the shutter

DiCaprio plays Teddy Daniels, a steely second world war veteran who arrives at a fortress-like island housing a hospital for the criminally insane in the gothic-tinged tale, which is based on the 2003 Dennis Lehane novel and co-stars Ben Kingsley, Mark Ruffalo and Max von Sydow.

The actor said he was more than capable of "switching off" once away from the shoot, but admitted there was often something of a "sombre mood going home every day" after filming his scenes on the wind-blasted Peddocks Island off the coast of Boston.

"This is the most challenging one to date for me. Physically yes, but emotionally more so," he said. "It was the nature of the material. It was obviously a complex jigsaw puzzle and it was surprising for both of us at times, and it really shocked us."

DiCaprio admitted it was hard for him to be completely candid about Shutter Island, due to plot twists unveiled during the course of the scary movie. "It's a very difficult narrative to talk about in detail because we want the audience to have that first experience," he said.

Scorsese said "the nature of gothic literature [had] opened the door" for the project to come into existence. He also credited such films as Otto Preminger's Laura, Jacques Tourneur's Out of the Past and John Huston's Let There Be Light, as well as Sam Fuller's classic 1963 B-movie Shock Corridor, as influences on Shutter Island.

"I don't know how else to tell the story except to utilise vocabulary like the rain, the darkness, the mansions, the framing, the lighting, and that sort of thing," he said.

"There's always the element of Shock Corridor hanging around the picture," he added. "But never specifically - it's more a case of it being conjured as a mantra."

DiCaprio described working with Von Sydow as "incredible." He said: "It was chilling to work with him. He is part of cinema's history and should be revered and respected as that. He is a genius."

Kingsley added: "He has absolute authority on the set. You can be chatting with Max on the set and Mr Scorsese will say ‘action' and you cannot see the difference between him being and him acting, even inches from him. It's an extraordinary quality, something essential and elemental about him."

Scorsese has now cast DiCaprio in every film he has made since 2002's Gangs of New York, but Kingsley said there was no "whispering in corners" between the pair on set.

"As another member of the cast observing this great longevity of a working relationship, you are never for a second excluded. Every debate on set between Martin and Leonardo is shared. There's no shorthand, so everyone on set gets the benefit of this working relationship and there's no private language. Given the history that's quite generous and remarkable," says Kingsley.