The Crown: Claire Foy and Matt Smith on the royal challenge of playing the Queen and Prince Philip

It was on that trip to Kenya that the 25-year-old princess found out that her beloved father, George VI, had died and that she was to become Queen. Despite the TV series graphically depicting the King’s final illness – coughing up blood and undergoing surgery inside the Palace to remove a lung – his death came as shock to his daughter. Her father was relatively young and she had planned to follow Philip to Malta for his naval career.

Elizabeth is played by Claire Foy and she manages to humanise the Queen while retaining a sense of mystique. The Oscar-nominated director Stephen Daldry (Billy Elliot, The Hours) who co-created the TV series along with Peter Morgan describes the British monarch as “the most visible, invisible woman in the world”, which must have been quite a challenge for the actress.

Queen Elizabeth II aged 27

“There is no first-hand account of what the Queen was saying or thinking, so my job as an actor is to interpret her circumstances,” says Foy. “To think of a young girl who didn’t want all that attention, who just wanted to be a good wife and mother and live in the country with lots of horses. And then suddenly she loses her father and gets the biggest responsibility in the world.”

Foy says the role got harder as the series progressed. “In the first two episodes, before she becomes Queen, I could be a lot freer with my emotions, but as the series goes on she develops an armour in order to cope with her circumstances. She has to be a sphinx, which must be so hard. Imagine never being able to shout shut up or cry, even in front of your own family.”

There’s nothing sphinx-like about Foy in person. She’s chatty, waves her hands around and has a very mobile face with huge expressive blue eyes. With no make-up, her hair scraped back in a pony-tail, wearing shorts with black tights underneath, Foy looks considerably younger than her 32 years. In contrast, there’s an inscrutable, regal stillness to the way she portrays the Queen.

“She’s much more solid than I am, she’s a horsewoman so her stance and energy is very centred, very still.” Did she spend a lot of time watching footage of the monarch?

“As an Englishwoman you pick up a lot through osmosis. I’ve been watching the Queen all my life. But, yes, I did watch news footage and was able to pick a couple of little tics. For instance, she plays with her hands a lot and has a certain way of holding them on her lap when she’s in public.”

There are strong parallels between the first series of The Crown and ITV’s recent Victoria. Both follow young women as they ascend the British throne. Both are love stories. Philip Mountbatten – played by Matt Smith with bleached blond hair – was a tall, dashing naval officer with whom Princess Elizabeth fell head over heels in love and insisted on marrying despite opposition at Court. Like her great-grandmother, Queen Victoria, Elizabeth promised to honour and obey her spouse during their wedding ceremony, but then struggled to find a proper role for him afterwards.

Peter Morgan’s script portrays Philip as a man who struggles with life in his wife’s shadow. At times his behaviour is pretty appalling. In the early years of their marriage, he’s shown coming home drunk after nights on the town and sulking like a bored teenager when forced to attend certain official functions.

Prince Philip aged 26

“I feel real sympathy for him,” says Matt Smith. “So much changed after George VI died. He was a respected naval officer and then suddenly he has to give it all up and walk two steps behind his wife. He was completely emasculated.”

Smith plays the young Duke of Edinburgh like a classic 1950s rebel in polo necks and a leather jacket with a blond James Dean quiff and a testosterone swagger. Was he really like that? “If you look at his body language,” says Smith, “I think he was a bit of a rebel and a moderniser. He married into a family ruled by protocol and tradition and he challenged the grey moustaches who ruled the roost at Buckingham Palace.”

The Crown is more grown-up than ITV’s Victoria, less Downton Abbey and more The West Wing. Peter Morgan focuses as much on Downing Street and Westminster as he does on the power struggles in the royal bedchamber. Not surprising when you consider Morgan’s earlier work. His 2006 film The Queen (starring Helen Mirren) delved into the royal family’s reaction to the death of Princess Diana.

In fact, The Crown producer Matt Byam-Shaw compares Claire Foy to a young Helen Mirren. “She’s extremely hard-working and professional. There’s a lot of pageantry in this series. It’s one of the biggest TV sets I’ve ever seen, with hundreds of people – actors, extras and crew – and she’s at the centre of it. It’s very rare to see a young actor with such poise and leadership.”

Smith, who had never worked with Foy before, was also struck by her poise. “When Claire’s in full regal costume you can’t help but treat her like a Queen.” The two clearly got on.

What makes Foy’s achievement even more remarkable is that she commenced filming just four months after giving birth to her first child. “I managed to carry on breast-feeding, which I’m really proud of. My daughter came with me everywhere and the production company were incredibly supportive, but I was existing on very little sleep and my body and my mind were still full of hormones.”

To Make Matters more complicated still, three months into the eight-month shoot, Foy broke her elbow after tripping over at a friend’s wedding. “I wasn’t even drunk!” she says, head in hands. “It was so embarrassing phoning the producer to tell him. I had to go back to work because we had these huge scenes to shoot of the Royal Wedding and the Coronation at Ely Cathedral. I was in a lot of pain until I went to see this amazing doctor who syringed all the blood off my elbow and reduced the swelling. But getting into the costumes was tricky for quite a while.”

Netflix is banking on a worldwide fascination with what goes on behind the gates of Buckingham Palace. Both the lead actors admit it’s made them feel differently about the royal family. “I live in London and frequently drive past Buckingham Palace, but I never gave them much thought in the past,” says Smith. “Now when I drive past I know that inside there are real people, a family with the same ups and downs that we all go through.”

The Crown writer Peter Morgan: how I get inside the mind of Queen Elizabeth II