From her note-perfect performances on the big screen to her stylish turns on the red carpet, everything about Dame Helen Mirren oozes confidence.

It comes as a surprise then, to learn the 69-year-old, who picked up an Oscar for her portrayal of Elizabeth II in 2006's The Queen, doesn't feel so self-assured.

"I don't really have confidence, honestly," Mirren confesses. "And certainly when I was younger, I was fraught with insecurity, sometimes paralysingly so."

The notoriously fickle field of acting isn't the obvious career choice for someone gripped by insecurity, but the star - currently appearing in new film Woman In Gold - believes it was the best move for her as a young woman.

"I think that's why I became an actress - you have to overcome that, you have to fight through it and come out the other side. Also, I think, as you get older, a lot of that anxiety just drops away. And it's a lovely thing."

Mirren turns 70 on July 26 ("it's Mick Jagger's birthday too, and the anniversary of the Cuban revolution - some year I'll have to go there for it"), but she hasn't given the milestone much thought.

"Every day's a milestone. So the fact that it's this particular day, as opposed to a week's time, is totally irrelevant to me. You just roll on through life," says the actress.

As for the 'sexy' tag which so frequently accompanies her name, she regards it as "such an easy, lazy" label.

"We're all so much more complicated than that," she adds. "There are so many different kinds of attractiveness in human beings, in human behaviour. I would like to see that recognised more often."

Indeed, Woman In Gold is more twin sets and pearls than sultry looks, as Mirren plays eighty-something Maria Altmann, an Austrian Jew who was forced to bid farewell to her family and flee Vienna during World War II.

Sixty years later, in the late Nineties, having relocated to Los Angeles, Altmann enlists the help of young lawyer E Randol Schoenberg (Ryan Reynolds) to try and retrieve the family's treasured possessions seized by the Nazis. Among the items is painter Gustav Klimt's prized Portrait of Adele Bloch-Bauer I (described in the film as "the Mona Lisa of Austria"), which is hanging in the Belvedere Gallery in the Austrian capital.

For Altmann, who died in 2011 aged 94, the struggle was about more than just reclaiming a painting from the Viennese bureaucrats determined to keep the treasured piece in Austria.

"Oh, so much more," Mirren agrees. "Yes, it was worth a lot of money, but [it's also the idea that] 'no, it doesn't belong to you, it belongs to me. It's what I grew up with and you have stolen it.'"

While her character had a troubled relationship with her home town, London-born Mirren was warmly received in Vienna and was even presented with a medal for services to the city by its mayor.

"I don't think they were really giving it to me, they were giving it to Maria Altmann. The mayor said to me that, above all, Maria's efforts to reclaim the paintings had made the city of Vienna face up to the past."

The daughter of a Russian father and an English mother, Mirren's paternal Russian family, exiled after the 1917 Revolution, also knew what it felt like to leave everything behind.

"My grandfather [a tsarist] lost everything. My Russian family were forced out of their home and had to go and to live in one room of an apartment in Moscow, five of them, with my grandmother dying of stomach cancer. It must have been absolutely horrendous," she says.

"But they were not taken away to concentration camps. I'm not saying there was not unbelievable brutality in Russia during the revolution, there was, but it didn't particularly happen to my family in that way."

Mirren, whose career began as a teenager at the National Youth Theatre, is currently depicting the Queen again in The Audience on Broadway, a production she originally appeared in on the West End stage (she recently ruled out playing the monarch again in Netflix's upcoming drama The Crown, stating, "we must all move on, and me most of all").

"Acting is the only thing I could imagine doing," says Mirren, who's married to director Taylor Hackford.

"I mean, maybe I would have been happy like the Queen, living on a farm, far from anywhere with lots of horses, dogs and children all running around, mucking in, getting grubby; those are the lines I say in the play.

"I guess I could imagine doing that. I love gardening, I love the countryside, I love the British climate."

When talk turns to the thrill of the stage, however, it seems highly unlikely Mirren will quit acting any time soon.

"There's something very magical about an empty theatre," she enthuses.

"I find it the most powerful, moving, incredible place to be. I love walking out on stage before I do the show and looking out at the empty seats, thinking, 'You're mine! All mine!'"

:: The Woman In Gold is in cinemas now.