With every newspaper’s front page a potential storyline and the public beginning to ring-fence Mondays at 9pm for its weekly dose of espionage thrills, Spooks had entered the TV zeitgeist. Eschewing the US showrunner model, the show powered on with Kudos’s Jane Featherstone, her producers and an ever-rotating team of head writers constantly tweaking the formula without sacrificing the style.

Macfadyen: We started shooting in late 2001, just after 9/11, and did an episode (‘I Spy Apocalypse’) where we simulated a disaster and went into lockdown. That exact story was on the news.

Agutter: Suddenly it was so timely because it was the first we were hearing about Al-Qaeda and suicide bombers.

Featherstone: It was a terrible zeitgeist to be in but it’s television’s job to reflect the world around it.

Nulluri: From the get-go the core of every episode was this idea about choosing the lesser of two evils.

Agutter: I was intrigued by this idea of blurred morality. I used to say, “Well, is my character good or bad? Which way are we going with this?”

Featherstone: You’d find yourself talking about very serious things, then you have to burst the bubble a little bit. You’re only making television. The writers’ rooms were hilarious places. We’d make up preposterous stuff.

Jonathan Brackley (writer): My fondest memories will always be sitting with the other writers and producers figuring out what the next big geo-political issue would be and trying to feed that back into the show. We were fans of the show from before we were even writing professionally, so it was a dream gig.

Featherstone: [Screenwriters] David Wolstencroft and Simon Mirren brought us into contact with great ex-spies. A lot of what you see in the first series was inspired by real-life incidents.

Nalluri: Even the fake dog poo used for dead drops was a real thing. It’s the most bonkers idea, but then again, no-one’s going to pick up a dog poo. We’d also heard this story from ex-spies where [agents] had gone into a house and the cat had escaped and it was raining outside, so they’d had to blow-dry it to cover up the break-in. We thought, “Are you kidding? We’ve got to do this.”

Macfadyen: Especially early on in Spooks, it wasn’t running around with guns, it was really mundane tradecraft. It was much more le Carré than Bond.

“From my first scene there was something between Ruth and Harry. You can’t help finding yourself flirting with Peter Firth!”

Nicola Walker

Nalluri: Peter was so good as Harry Pearce that people started writing for him and his role became bigger and bigger and bigger.

Hugh Simon (Malcolm Wynn-Jones): I saw Malcolm as the Thunderbirds’ Brains character, with a touch of Q.

Norris: Ruth is my favourite character. I thought Nicola Walker was great, and I loved Gemma Jones (treacherous agent Connie James). There were some great female characters in Spooks.

Richard Armitage (Lucas North): I loved working with the character of Ros and working with Hermione [Norris]. If you look at Robin Wright in House Of Cards, I feel like she’s watched Hermione in Spooks. She’s just a cool character.

Firth: [Harry’s chemistry with Ruth] was manna from heaven to show his human side. There was nothing scripted between Ruth and Harry when Nicola arrived in the second series but we were flirting away. There’d be moments where a look was held too long or there’d be a blush.

Walker: You can’t help finding yourself flirting with Peter Firth, I’m sorry! From my first scene, which was me coming and dropping files, there was something there between Ruth and Harry. The writers started to spot something that was happening between me and Peter on camera.

Firth: It was always good to have new talent coming aboard, because it would shift the dynamic.

Norris: As an actor [joining an established show] you think, “Where’s the show at? Is there still enthusiasm for it?” When something’s been around for a while, it can wane. That was not the case with Spooks.

Rupert Penry-Jones (Adam Carter): I was in an antiques shop when Jane Featherstone, an old friend of mine, came in and we got talking. I’d seen Spooks and knew what a huge success it was and said, “Hey, why didn’t you ever get me in for a meeting?” And she said, “Well, it’s funny you should say that because Matthew’s leaving. Would you be interested?”

Norris: Walking onto a show that people clearly love makes you anxious. It’s like your first day at school.

Penry-Jones: My first scene was me doing a drunk, homeless man with a terrible Scottish accent. It’s funny coming in when everyone is so close and their main guy is leaving. But they were all really nice and I’m still friends with them all.

“I’d never seen a crew work like that, before or since: really fast, really on it. It felt like you were making something excellent.”

Hermione Norris

Firth: We shot the first series at a disused hospital in Kensington, then for the second series we moved to Pinewood. We thought, “Hurrah, we’ve arrived!” But that was too expensive so they built a studio in the old Peek Freans biscuit factory in Bermondsey.

Norris: I’d never seen a crew work like that, before or since: really fast, really on it. It felt like you were making something excellent.

Armitage: I’d never really watched the show until I signed up. I got sent the box set and thought I’d watch one episode, then it’s 5am and I’m going, “One more, just one more.” You couldn’t watch just one episode.

Nalluri: We constantly shot with three cameras and our edit rate was much faster than what was on television at the time.

Firth: We’d work for five months per season with an 11-day fortnight. Twelve hours was a standard day but it would often be 15. If you’re shooting on a tight budget every day costs money.

Penry-Jones: I was in hospital while my wife was giving birth to our second child and they rang up and said, “If he’s born in the morning can you get back in the afternoon because we’ve only got this location for a day?” I sort of said, “Oh, I suppose”. My wife went mental and they rang back and said, “Actually, don’t worry. We’re being stupid.”

Norris: I was having babies through this time and I look back and think, “Oh my God, having water torture and being blown up when you’re seven months’ pregnant…” I’d learn all my stuff while I was in the car on the way in and out.

Simon: It was very much Kudos’s baby initially, but once we got into the third series it was obvious to the BBC that it was going to run and run. That’s when people started interfering with scripts, which did become frustrating over the years. I’ve seen directors tearing their hair out at great, thick memos they’d received from Level 7 at the BBC.

Firth: You certainly got the feeling that things got a bit disjointed, but you know what? As an actor, you have some power because nobody’s really listening. There isn’t time to listen to the intricacies of the dialogue, so you can say things that make it work.

Simon: My character would change from week to week depending on who was writing the series, even down to his sexuality. If a certain writer was writing, he'd make Malcolm gay. I gave up worrying about it.

Firth: The plots were dense and if you were shooting four simultaneously, good luck. But as long as someone was keeping track of what suit I was supposed to wear, I was fine.

Armitage: The scripts would come in really late, which was exciting and frustrating, but it meant they were keeping their finger on the political pulse. It’s why the show ran for ten years.

Firth: The burn-out rate of continuity people was quite high.

Norris: It wasn’t easy dialogue to learn, because remembering facts and information isn’t the same as doing a drama. It’s a very different skillset.

Walker: I felt very sorry for them but Ruth Evershed was a slightly different creature – a luddite who’d often use pen and paper &nash; so I could have my lines written in the files. You’d slip a page in and it would say, “He arrived at 12.21pm…” (laughs). I’d argue that this was all information that she wouldn’t know off by heart.

“I defy anyone not to enjoy doing a handbrake turn and throwing a stuntman out of a car in the middle of the West End.”

Matthew Macfadyen

Norris: We’d laugh a lot because it was an incredibly pressured job. It got pretty hysterical.

Walker: Peter and I would take our scenes so seriously, but between takes Peter would be whispering the most unrepeatable things in my ear. He was always stopping you from being so serious you’d disappear.

Nalluri: The entrance pods [on The Grid] are actually from Thames House, but they have 20 of them and we had two and a bloke on a bicycle in the cupboard cycling. We’d get stuck all the time. Hence no pods in the movie.

Firth: You’d have high stakes and tension and a bomb about to go off and there’d be someone in the background going, “This fucking door!”

Macfadyen: My favourite moment was probably doing a three-point turn on Great Queen Street and throwing a body out of the car on an icy day. I defy anyone not to enjoy doing a handbrake turn and throwing a stuntman out of a car at 2am in the middle of the West End.

Norris: I loved all the physical stuff. I loved the driving. Ros had some great one-liners and speeches.

Armitage: The one thing I love and miss about Spooks – and I really do miss it – was exploring parts of London that you’d never normally see, like Lucas’s first scene in Battersea Power Station. They never shot in the same place twice.

Nalluri: The geography [of the show] was all very thought out, with the Thames as the central geographical area. I was trying to find wide landscapes, which is really hard in London, and the one place I could find them was on the bridges by the river.

Simon: It sounds flippant but my favourite part was having large amounts of money going into my account quite regularly after 20 years of being a jobbing actor. Believe me, it made a big difference in my life.

Penry-Jones: I just loved the part, playing someone so heroic. And the people just felt like a big family.

Walker: [With Spook fans] it was just glorious. They use to sidle up to me on the Tube and say, “The white falcon will land at 12.10.” I don’t think anyone ever said, “Oh, I love Spooks.”

Simon: Spooks fans were lovely. I still get the odd letter.

Nalluri: We’d heard that the hits on [the MI5] website were going through the roof and that were inklings that people there were really loving it. They invited some of the cast and the crew around season five or six to say hello and apparently it went down a storm. They are huge fans. I suppose it makes them look great.

Featherstone: Except MI5 would get the wrong sort of applicants. They want intelligent, thoughtful individuals, instead of people thinking they were just going to get to kill people and have car chases. We messed it up for them.