In the middle of answering a question about her experience with comic book fans, Scarlett Johansson is given a glass of tomato juice. “Don’t worry, it’s not a Bloody Mary,” she says. “Or maybe it is,” she adds, mischievously. “I had it on the plane over here and I just really liked it.”

“Is it a craving?” I ask, sitting next to her in London’s Dorchester Hotel where the film is having its premiere that night.

“No, that’s a silly question,” she says, as she moves on to carry on talking about the devotion to the Marvel fans around the world have shown.

Perhaps, but it’s an innocent one. The 29-year-old actress has yet to confirm her pregnancy herself, but Marvel producer Kevin Feige let it slip a few weeks ago, and since then, Scarlett has already found herself topping lists about pregnant women in Hollywood. She and fiancé French journalist Romain Dauriac are believed to be in the early stages of expecting, and Scarlett is still on track to film The Avengers sequel in April.

Pregnancy is just one of the many roles Scarlett, who has been nominated for four Golden Globes since she started acting at the age of 10, currently has. Her honey-warm voice helped earn Her a best picture Oscar nomination, she’s currently enjoying critical acclaim with the indie movie Under the Skin, which premiered at Sundance earlier this year, and now, Captain America: The Winter Soldier, which releases this weekend, sees her slip back into costume as Natasha Romanov, aka the Black Widow.

In The Winter Soldier, Scarlett reunites with Robert Redford, who witnessed the early part of her career when they were in The Horse Whisperer in 1998. Scarlett, who was born in New York City and studied threatre there, was 13 then. “It was nice to meet him as an adult; he was just as pleasurable as I remember,” she says. “He has a real natural way about him in life, and in his performance. I never thought I’d be holding a gun to his head though!”

Dressed in a blue suit with a red-and-blue patterned silk shirt, she looks casual with her hair swept up in a pony,every bit of the easy-to-work-with, anti-diva her co-stars Samuel L Jackson and Anthony Mackie describe. Her role as the Black Widow has made her part of the billion-dollar franchise – a success that superseded the industry’s expectations. The Avengers became the fastest film to gross $1 billion, and the third-highest-grossing film in movie history. Does she feel any of that pressure for the sequel, which is due out next year? “ [Director] Joss [Whedon] is supposed to experience all that pressure,” says the actress, chuckling.

“For me, one of the exciting things about doing a film like this is that you have the challenge of keeping the character fresh, while still maintaining the integrity of what the audience loves about them,” she says. “Even doing theatre doesn’t compare to this,” continues the Tony-Award winner. “You have a relationship with the audience, because you’re coming back to them. I like that, because it’s an opportunity that we don’t always have as actors.”

The key to playing a superhero, Scarlett says, is confidence, even though she admits there’s a bit of fake-it-til-you-make-it. “The most important thing is you just have to drive it like you own it, so even if you feel goofy doing it, if you sell it with conviction, and add some music, it’ll look cool.”

“The most important thing [to playing a superhero] is you just have to drive it like you own it, so even if all you feel goofy doing it, if you sell it with conviction, and add some music, it’ll look cool.”

No doubt she’ll be channelling that while filming Avengers 2: Age of Ultron, which shoots in London, although the production team has been filming some of the set-up shots in South Africa. “South Africa is really beautiful, I’d love to go there,” she says. “There are so many of us, so who knows where, if anywhere, we’ll be going. But I think we’ll just be here [in London].”

There’s talk that Black Widow may get her own movie one day soon. “The material is certainly there, she says. “And it’s great to have a female-driven superhero who is not just a character taking every opportunity to pose sexy but actually has some substance to her.” Scarlett loves seeing women at Comic Conventions rocking the Black Widow costume. “It’s not an easy one to pull off,” she says. “I’m always, like, ‘you go, girl! And I love it when my friends’ daughters dress up as her. It’s great that they have someone who can go head-to-head with the guys and is witty to look up to.”

“It’s great to have a female-driven superhero who is not just a character taking every opportunity to pose sexy but actually has some substance to her.”

While the Black Widow may or may not get her own movie, Scarlett will be getting hers. The actress will direct her first feature-length movie, based on a Truman Capote novel called Summer Crossing. New mother and new director – true to Scarlett’s definition of superhero.