Nothing beats a brilliantly-executed bedtime story, but growing up to play one of the characters from that story comes close. Ditching his Sherlock coat for dragon scales in the new Hobbit film, Benedict Cumberbatch tells Keeley Bolger why landing the role is the best thank you he could have given his dad.

Nasty. Satanic. Creepy... Not really the sort of words usually associated with man of the moment Benedict Cumberbatch, but these are the adjectives the actor's chosen to describe his latest character, the monstrous dragon Smaug in The Hobbit: The Desolation Of Smaug.

"Smaug is the ultimate symbol of the corruption of power," says the 37-year-old star. "He's a sleepy serpent on top of his pile of gold. It brings him nothing but a damp, dank retirement, no joy or humour. He's vainglorious and proud of his own power and wealth, but it has essentially ruined him."

In the second part of the blockbuster trilogy, which is set in Middle-earth 60 years before the time of The Lord Of The Rings, a younger Bilbo Baggins, played by Martin Freeman (he was older and played by Ian Holm in the 2001 film), journeys with the wizard Gandalf and thirteen Dwarves on an epic quest to reclaim the Lonely Mountain and the lost Dwarf Kingdom of Erebor - oh, and slay Smaug while they're at it.

Of course, Cumberbatch and Freeman are old pals, having starred together as Sherlock Holmes and Dr Watson in BBC One's Sherlock since 2010. But this time, while Freeman, albeit in rather distinct costume, is recognisable on screen, Smaug is CGI-animated, so Cumberbatch did his acting in a recording studio.

Getting the dragon's voice just right was very important.

"I was trying to articulate certain things which are impossible, because I'm a mammal trying to be a reptile," he recalls, laughing. "It had to sound like he had the growl of an atomic explosion."

There were other, rather unhygienic factors at play in the making of Smaug's voice, too.

"It had to build that bridge between animal and human, something guttural, deep and rasped, kind of dry as well because of all the fire breathing," says the actor, who worked with a dialect coach to perfect his performance. "I don't think Smaug's cleaned his teeth in a while," he adds. "He's got goat and dwarf breath."

As unpleasant at that sounds, it's unlikely to dent Cumberbatch's present appeal. Since his breakthrough role as the eponymous detective, the London-raised actor can barely put a foot wrong.

He's had leading roles in The Fifth Estate, as WikiLeaks founder Julian Assange, Star Trek: Into The Darkness as Khan, plus War Horse, and then there's the upcoming drama August: Osage County, with Meryl Streep.

Needless to say, he's been a hit with female fans too, and even has a 70,000-strong Twitter group following who call themselves the 'Cumberbitches' in his honour. Though when the actor found out about them, he asked them to refer to themselves as 'Cumberpeople' or a 'Cumber collective'.

Despite all of his credentials, when it came to filming The Hobbit, he was studious, especially when he considered the performances of other actors before him.

"I'd never worked with motion capture before," he says. "I know I'm not Andy Serkis doing amazing, pioneering and masterful work as Gollum. I'm going to be mucking around as a serpent, and wriggling around on the floor trying to articulate things I can't do."

CGI may have been new to him, but the tales of Bilbo and co were certainly familiar.

As the only child of two actors, a young Cumberbatch was treated to some tantalising bedtime stories, and one in particular stuck with him - The Hobbit.

"I was about six or seven at the time, but he [his father] definitely sowed the seed," the actor, who later attended the prestigious Harrow School, notes.

"He's a great, great, great voice artist; he's a great actor, so he installed a love for literature in me, actually.

"[My father reading me The Hobbit] was the first time I'd ever heard the written word, and I had an explosion of imaginary landscapes in my head and thought, 'Wow, that can come off the page of black and white, that's insane'," he continues, recalling his father, Timothy Carlton's influence.

"He used to do the most extraordinary characterisations, not just as Smaug but Gollum and Gandalf and the hobbit himself. It was a very rich way to be introduced to such an incredible book.

"So, when you can go home and say to your dad, 'I'm playing Smaug, and I've got you to thank for it', it's a very satisfying day in an actor's life."

More than three decades on, he's still grateful for the part his father played in steering his career path.

"Seriously, I owe a lot to my dad, so in a way, this feels a bit like an homage to him," Cumberbatch adds, smiling. "Or at least a doffing of my cap with some welly and gusto."

Extra time - Making the movie

:: To create a snowy effect in Lake-town, the entire set was covered in snow made of Epsom salt, with wax sheets of film ice floating on the water pool below.

:: The forest of Mirkwood contained 32 craggy trees, each reaching 30ft.

:: Smaug is the size of two 747 airplanes.

:: The team built a 40ft studio filled with gold.

:: The digital team had to create 20 million coins at a time to cover Smaug, who sleeps in a gold-filled lair.

:: Rising star Ed Sheeran, 22, sings I See Fire on the film's soundtrack.

:: The Hobbit: The Desolation Of Smaug is released in cinemas on Friday, December 13