It's the end of a long day of interviews for Benedict Cumberbatch and he seems almost giddy as he gazes wishfully out of a hotel-room window in Toronto. Suddenly, he says excitedly: "I was in the elevator with Bill Murray yesterday. It was f---ing fantastic! I stepped into the elevator in a bathrobe and he went, 'oh this guy is up for the same underwear ad that I am.' And then he stepped over to me and whispered, 'You won't get it, I've already got it."

"He was so funny, I was completely starstruck."

These days it's usually the other way around when the 38-year-old actor walks into a room. In the past three years, Cumberbatch has graduated from being known mostly for stage work in his native England to a name brand whose films have included best-picture Oscar winner 12 Years a Slave, the Meryl Streep dramedy August: Osage County and the Julian Assange story The Fifth Estate.

This year the actorhas all his eggs in one basket here at the Toronto Film Festival, but what a basket. He's an Oscar favourite and Golden Globe nominee for his complex role in The Imitation Game as English mathematician Alan Turing, who virtually invented the first computer and during World War II broke the enigma codethat helped end the war years earlier, only to be persecuted by his own country later for being homosexual.

It's not the first time Cumberbatch has played a character much smarter than him, he admits. His title character in the television series Sherlock enjoys being a pompous arse and as Khan inStar Trek: Into the Darkness he's no dummy either. But nothing prepared the actor for the journey of Turing, who was finally issued an official pardon and apology from the Queen this year, 60 years after he committed suicide following his chemical castration for homosexuality.

"I got to know my character very well and by the time we shot the scene where he breaks down in front of Joan [Keira Knightley] at the end, I had no control over my emotions," he says. "I couldn't stop crying and it wasn't good acting, it was just because I knew that I was mourning this extraordinary human being who I had become so fond of. I can't remember another time that it's happened to me in my career, but it's a desperately moving story and it deeply affected me."

Asked about his own maths skills, Cumberbatch looks speechless. "My what? Oh, I thought you said my romance skills, as we sit here alone in an empty bedroom'," he deadpans, then chuckles. "Yes, I'll admit they are pretty awful and even now I vaguely panic when somebody give me arithmetic to do, because it's just not my strong suit."

The fiercely private Cumberbatch likes to waffle on in interviews about the intricacies of his character's motivations until he runs the clock down without saying anything too personal, I've discovered in the past. Today he's tired, so maybe his defences are down a little because he's surprisingly funny, even joking about how he navigates a world of being constantly watched and recorded.

"What's interesting is that you walk a minefield because everyone is a walking publisher, so anything you do in public isn't private, and it's all up for scrutiny," he says. "The funniest ones are the people who pretend they are on the phone so they can take a photograph and think you don't notice. I go right up to them and shock them by asking if I can see the picture!"

Catching up with Cumberbatch again last month, he was in Los Angeles doing his bit for his film's award chances but pining for some quiet time at home in London. "I like being in nature – that's why l live near the Heath, because I just love the fact there's ancient woodland on my doorstep in the middle of London," he says.

He'd just announced his surprise engagement to his girlfriend Sophie Hunter via a paid-for announcement in the classifieds section of The Times, naming both their parents.

"It's the standard way of doing it in England and it may seem old-fashioned now but I would have done that if I wasn't in this strange, heightened position that I am as a famous actor, so it's just to try and normalise something that's deeply personal to me I guess," Cumberbatch says.

Was he old-fashioned in his proposal?  "That's something for me to know and you to never find out," he says with a polite grin.

Much has been written about the actor and two friends being kidnapped in 2005 by armed robbers in South Africa, only to be released unexpectedly from the trunk of a car. He has been quoted many times as having promised himself at that time that if he survived he would live a life less ordinary. "Have I done that?" he jumps in, knowing where the question is going. "I would say I have done pretty well since then - "as he says in his empty hotel room!"

Being seen and heard

Benedict Cumberbatch can be seen in just one film this holiday season, but his voice can be heard in two others: as Smaug the dragon in The Hobbit: The Battle of the Five Armies (out December 26) and as Classified, the head of a pack of wolf spies aiding the black-and-white heroes in the animated Penguins of Madagascar (January 1).

"Penguins and dragons are very different animals, excuse the pun," Cumberbatch says of his voice work. "Because Smaug came out in motion-capture form, the movement completely informed the voice ... But the Penguins part was extraordinary in a different way because we recorded over a long period of time and had a lot of fun and freedom.

"All disciplines of acting feed off one each other and they all require different energies," he adds. "So I am not exhausting myself doing just one thing."

It's the end of a long day of interviews for Benedict Cumberbatch and he seems almost giddy as he gazes wishfully out of a hotel-room window in Toronto. Suddenly, he says excitedly: "I was in the elevator with Bill Murray yesterday. It was f---ing fantastic! I stepped into the elevator in a bathrobe and he went, 'oh this guy is up for the same underwear ad that I am.' And then he stepped over to me and whispered, 'You won't get it, I've already got it."

"He was so funny, I was completely starstruck."

These days it's usually the other way around when the 38-year-old actor walks into a room. In the past three years, Cumberbatch has graduated from being known mostly for stage work in his native England to a name brand whose films have included best-picture Oscar winner 12 Years a Slave, the Meryl Streep dramedy August: Osage County and the Julian Assange story The Fifth Estate.

This year the actorhas all his eggs in one basket here at the Toronto Film Festival, but what a basket. He's an Oscar favourite and Golden Globe nominee for his complex role in The Imitation Game as English mathematician Alan Turing, who virtually invented the first computer and during World War II broke the enigma codethat helped end the war years earlier, only to be persecuted by his own country later for being homosexual.

It's not the first time Cumberbatch has played a character much smarter than him, he admits. His title character in the television series Sherlock enjoys being a pompous arse and as Khan inStar Trek: Into the Darkness he's no dummy either. But nothing prepared the actor for the journey of Turing, who was finally issued an official pardon and apology from the Queen this year, 60 years after he committed suicide following his chemical castration for homosexuality.

"I got to know my character very well and by the time we shot the scene where he breaks down in front of Joan [Keira Knightley] at the end, I had no control over my emotions," he says. "I couldn't stop crying and it wasn't good acting, it was just because I knew that I was mourning this extraordinary human being who I had become so fond of. I can't remember another time that it's happened to me in my career, but it's a desperately moving story and it deeply affected me."

Asked about his own maths skills, Cumberbatch looks speechless. "My what? Oh, I thought you said my romance skills, as we sit here alone in an empty bedroom'," he deadpans, then chuckles. "Yes, I'll admit they are pretty awful and even now I vaguely panic when somebody give me arithmetic to do, because it's just not my strong suit."

The fiercely private Cumberbatch likes to waffle on in interviews about the intricacies of his character's motivations until he runs the clock down without saying anything too personal, I've discovered in the past. Today he's tired, so maybe his defences are down a little because he's surprisingly funny, even joking about how he navigates a world of being constantly watched and recorded.

"What's interesting is that you walk a minefield because everyone is a walking publisher, so anything you do in public isn't private, and it's all up for scrutiny," he says. "The funniest ones are the people who pretend they are on the phone so they can take a photograph and think you don't notice. I go right up to them and shock them by asking if I can see the picture!"

Catching up with Cumberbatch again last month, he was in Los Angeles doing his bit for his film's award chances but pining for some quiet time at home in London. "I like being in nature – that's why l live near the Heath, because I just love the fact there's ancient woodland on my doorstep in the middle of London," he says.

He'd just announced his surprise engagement to his girlfriend Sophie Hunter via a paid-for announcement in the classifieds section of The Times, naming both their parents.

"It's the standard way of doing it in England and it may seem old-fashioned now but I would have done that if I wasn't in this strange, heightened position that I am as a famous actor, so it's just to try and normalise something that's deeply personal to me I guess," Cumberbatch says.

Was he old-fashioned in his proposal?  "That's something for me to know and you to never find out," he says with a polite grin.

Much has been written about the actor and two friends being kidnapped in 2005 by armed robbers in South Africa, only to be released unexpectedly from the trunk of a car. He has been quoted many times as having promised himself at that time that if he survived he would live a life less ordinary. "Have I done that?" he jumps in, knowing where the question is going. "I would say I have done pretty well since then - "as he says in his empty hotel room!"

Being seen and heard

Benedict Cumberbatch can be seen in just one film this holiday season, but his voice can be heard in two others: as Smaug the dragon in The Hobbit: The Battle of the Five Armies (out December 26) and as Classified, the head of a pack of wolf spies aiding the black-and-white heroes in the animated Penguins of Madagascar (January 1).

"Penguins and dragons are very different animals, excuse the pun," Cumberbatch says of his voice work. "Because Smaug came out in motion-capture form, the movement completely informed the voice ... But the Penguins part was extraordinary in a different way because we recorded over a long period of time and had a lot of fun and freedom.

"All disciplines of acting feed off one each other and they all require different energies," he adds. "So I am not exhausting myself doing just one thing."