A year on, and The Crown is back for a second season. With Morgan again the creative driving force, this 10-episode follow-up covers the period from 1956 to 1964 as it plays out the royal family soap opera – notably difficulties in the marriage of Elizabeth (Claire Foy) and Prince Philip (Matt Smith) – against the backdrop of world history.

Early episodes examine Philip’s possible carousing overseas, when he was linked to various women. As Morgan put it recently, “Doesn’t everyone in Britain know he had an affair?”

“I didn’t and I still don’t know,” says Foy, cautiously. “I don’t believe we did see him philander,” adds Smith. “[There are] subtle allusions. I think with any story that is based on historical fact, it’s your duty as a dramatist to shine a light on things that are perhaps uncomfortable for a nation and an audience, and I think Peter Morgan does that with grace and skill.

“We’re not saying [that] it’s one thing or the other. We’re allowing you to decide.”

Of course, timing is everything – and The Crown’s second season arrives just a fortnight after the queen and Prince Philip celebrated their platinum wedding anniversary celebrating 70 years of marriage.

How Netflix is bringing cinema experience to Hong Kong homes, with sounds so real you’ll want to duck your head

“It is a wonderful bit of romantic serendipity,” says Smith. “If you look at them now … yes, we shine a light on things that are very difficult, as any marriage could endure if it lasts that long. But look at them – they look terribly happy at the moment.”

Other subjects examined range from the 1956 Suez Crisis to Baron Altrincham, whose outspoken criticism of the queen did more to help the monarchy modernise in the 20th century than anything else (and that includes the arrival of the queen’s now-traditional televised Christmas speech).

Then there are Margaret’s “dark nights of the soul”, as Kirby puts it, in the aftermath of her ill-fated romance with RAF Group Captain Peter Townsend, and her subsequent marriage to photographer Anthony Armstrong-Jones, aka Lord Snowdon. Cast as “Tony” is Matthew Goode (Brideshead Revisited).

“It was a long search to find Tony,” says Kirby. “He was the first person in her life that made her feel genuinely uncomfortable, and out of her depth. She walks into any room and most of the time she’s always the high status. Even with her sister, she’s much more dominant. So he’s the first person that unnerves her, so we had to find an actor that does that, and Matthew is very unnerving!”

It is the human elements of this royal story – Margaret’s troubled relationship with Elizabeth; her grief over the sudden loss of their father, King George VI, and her failed love affairs – that audiences have plugged into, says Kirby.

Foy admits that playing the queen across 20 hours of television drama has given her fresh insight: “My understanding of her now is not as a monarch, it’s as a human being. It’s also a fictionalised version of her. But I do know the facts of her life more than I ever did before. So it’s given me the opportunity to think about what this woman has felt in her life. I hope that is what the show does; you mustn’t take people for granted generally in their lives.”

Likewise, Smith has grown fond of Philip. “I feel I understand him more emotionally,” he says. “I defend him to the hilt.”

He even compares him to Dr Who, the perennial sci-fi character he played for four years. “They’re both aliens in their own environment. They’re both outsiders. They’re both going against the grain. They’re both rebels. They both do what they want, when they want, how they want. They never ask permission. I genuinely believe there are a lot of similarities.”

Intriguingly, the current actors are now set to bow out, with an incoming cast taking over the roles as the characters age for the next season.

“We always knew it was only going to be a couple of years,” says Smith, whose role as Philip has yet to be recast. The only confirmed replacement is Broadchurch star Olivia Colman, who will play Elizabeth. “Oh my God, I can’t wait!” Foy says. “Can’t wait. I sort of want to be there…as a fan! But I don’t think that would be helpful.”

Netflix dumps Kevin Spacey over sexual assault allegations as New York police close in on Harvey Weinstein

Word has it from sources that in the real royal household, the queen has watched the show but Prince Philip declined. Foy admits she would be reluctant to meet the queen now; unlike her recent role in the movie Breathe – where she met Diana Cavendish, the woman she played – she had no such blessing from the queen.

“She could completely turn around to me and say, ‘I really don’t like what you’ve done.’ And she’d be completely entitled to.” Then again … she might love it.

The Crown Season 2 is available on Netflix from December 8