Kit Harington on Game of Thrones fame, his ancestry and what he’d do if he were prime minister for a day

There are GoT fansites devoted to analysing whether the precise inflection of Harington’s hair might hint at possible plot twists. There are photoshopped images showing what he might look like with a shaved head. There are style guides on how to achieve his tousled curls (“While blow-drying, use your fingers to twirl strands and get that curling action going”).

Harington, 30, finds it all a bit mystifying. “It’s bizarre,” he says, sitting in a light-filled room in east London, dressed all in black and sporting a pair of owlish spectacles. He confesses he’s looking forward to a haircut once the next, final, season has filmed, “but I have to keep it like this until then”.

Luckily, in the meantime he’s found another role that requires a healthy head of hair. In BBC1’s three-part drama Gunpowder, about the 1605 plot to blow up Parliament, Harington plays the ringleader Robert Catesby and his hair is long, luscious and reassuringly 17th century. “I looked at pictures of Catesby and, well, I can’t deny he had a beard and long hair,” says Harington, who is also an executive producer.

But the connection went beyond the purely follicular: Catesby is one of Harington’s ancestors on his mother’s side. He grew up in Acton, west London, being told by his parents all about the nefarious activities of his forebear. And Catesby is his middle name.

It was Catesby who led the plan to bomb the House of Lords in protest at King James I of England’s relentless persecution of Catholics. Catesby’s co-conspirators included Guy Fawkes, who was arrested guarding barrels of explosive after an anonymous tip-off. The foiled plot is still commemorated every year on Bonfire Night, when effigies of Fawkes are burned.

Harington couldn’t understand why the story of his ancestor had never before been dramatised, and so decided to do it himself. He put together an outline with his friend, Daniel West, and sold the idea to Kudos, the production company behind Spooks. The cast includes American actress Liv Tyler (“She does a fantastic English accent”) and Sherlock star Mark Gatiss.

The script was written by Northern Irish author Ronan Bennett (Top Boy) and he doesn’t shy away from depicting the brutal aspects of the era: in the first episode, a priest is beheaded and Catesby’s aunt is stripped naked before being crushed to death on a public scaffold.

“Yeah, that’s historically accurate,” Harington says. “I think it was important to us – that brutality – because it sets Catesby on a very specific path. We need to understand why this man goes about putting together a team to carry out this act. We need to understand what pushed him to that place.”

Although set more than 400 years ago, Gunpowder is a story with modern relevance: a group of disaffected young men, driven by religious zealotry, plan what is essentially a terrorist act. Was Harington aware there could be certain parallels made with the recent atrocities committed by Islamic extremists?

“We understand that there is obviously a modern resonance with terrorism,” he says carefully. “But we are not using the term ‘terrorism’ because they weren’t terrorists. A terrorist is someone who goes and plants a bomb or causes a terrifying act to frighten a population and therefore push the government to do something. These guys were revolutionaries. They wanted to bring down governments so they could then put a new government in place. So, they weren’t technically terrorists.”

Yes, but it’s often said that one person’s terrorist is another’s freedom fighter. “It’s true it could have real resonance among an audience, in that they see a group of young men who were disenfranchised, who go and decide to do a very violent thing, and who decide to kill people for what they see is the greater good,” Harington says. “You do see that on our news.”

Despite his Catholic ancestry, Christopher “Kit” Catesby Harington was raised in the Church of England but isn’t particularly religious. His mother, Deborah, was a playwright, his father, David, a businessman, and his earliest ambition was to be a writer: “I was a complete mummy’s boy and wanted to write just like Mum did.”

When he was 11, the family moved to Worcestershire and Harington and his older brother, Jack, attended the local state school. It was there that he discovered a talent for acting, thanks in part to the efforts of his drama teacher, Sue Hickman (sweetly, he specifically asks me to mention her in this piece). He liked drama, “because I’m a massive show-off and that sort of turned into a love for it”.

Harington went on to study at the Central School of Speech and Drama, where he landed a role in the original stage production of War Horse at the National Theatre. After graduating, he auditioned for a part in a new HBO drama set in a fantastical world inhabited by dragons, giants and an army of the undead.

“I didn’t know what it was going to become,” he says. “I think I knew there was something different and interesting about it, but right then I wasn’t in a position to pick roles. It was just this TV show, it was American and it was HBO. So I said yes.”

The show was Game of Thrones and it has changed his life, not least because the actress who played his love interest, Rose Leslie, is now his fiancée. “I don’t talk about my relationship,” he says politely, “but me and Rose are very happy together and we live together and yeah, it’s all good.”

Game of Thrones also made him hugely famous. He recalls a trip to LA shortly before the sixth season aired, and finding an enormous billboard with his face on it covering one side of a skyscraper. “It was so surreal. It blows your mind something like that.” Did he take a photo of himself next to the billboard? He grins. “Yeah, of course!” He laughs. “Would have been rude not to.”

In “Thrones”, as Harington calls it, Jon Snow is the moral compass: brooding, intense and reluctant to claim the power that is rightfully his. Harington thinks one of the core messages of the show is that the people who most want power are the least deserving of it. “I think that’s the problem with politics,” he says. “At the heart of it is that, if you want to be a politician you probably crave power and therefore you probably shouldn’t be a politician. And that’s just a natural human condition I’m afraid. I’ve always thought maybe we should choose politicians almost like we do jury service: ‘You’re going to be prime minister and you got randomly selected.’”

What would Harington do if he were prime minister for the day? There is a long pause. “I would pump more money into state education.”

One of the interesting things about Harington is that despite his blue blood – his father is a Baronet; and Wikipedia states that he’s a direct descendent of Charles II, although Harington has no idea if that’s true – he has escaped the “posh actor” tag often applied to contemporaries such as Eddie Redmayne, Tom Hiddleston or Benedict Cumberbatch.

“Well, I didn’t go to Eton,” Harington says. “My parents weren’t wealthy, we didn’t have a huge house. I went to state school… I’m proud of my family history but I don’t think of myself as posh. It’s an outdated term anyway and should become more outdated.”

I ask him whether he worries that it’s harder for people from less privileged backgrounds to become actors and he becomes more animated, leaning forward in his chair, tucking his hair behind his ears as he talks.

“The wealth gap affects this industry as much as it affects any industry, and more so. You can’t be an actor if you need to hold down another job… It’s much easier to be an actor if you have an independent source of wealth. If I hadn’t got the job straight out of drama school I would be screwed because my parents couldn’t have supported me through trying to find work.

“But I think it’s deeper than that. The reason people like Eddie Redmayne and Benedict Cumberbatch continue to work, is because (a) they’re incredibly talented actors, and (b) they were given the resources by their educational system to go into that and to have every chance of success.

“I really believe if we’re looking at trying to get more and more underprivileged people into the creative industries, and acting especially, it needs to start at government level through funding. And I think right now the arts in schools are just going completely underfunded.”

He’s so passionate on the subject, I wonder if he’s ever been interested in a political career, but he says all his future projects are to do with acting or producing. It’s a shame, though. If Harington stood for prime minister, he (and his hair) would get my vote.

Gunpowder begins on Saturday 21st October at 9.10pm on BBC1