Slow Horses writers on taking Slough House from page to screen and the show's future

Ahead of the new season, and an appearance together at Theakston Old Peculier Crime Writing Festival (17th - 20th July), Herron and Smith spoke exclusively with Radio Times about how the adaptation first came together, how the process has worked from book to screen, and where the series is set to go next.

On recalling his first meetings about adapting his Slough House novels, Herron reveals he had meetings with three different production companies in one day back in 2014 - but what he remembers it for is the weather.

"I got absolutely drenched getting to the railway station," he says, "and I spent the first two meetings of the day basically dripping on the floor and gradually drying off.

"The third meeting of the day was with See-Saw and I was dry by then, so I was in a good mood, and I went with them."

Smith notes that "getting drenched on the way to a meeting feels very Slow Horses", to which Herron says: "Absolutely."

For those who haven't yet dived into the world of Slow Horses, either in literary form or on screen, the series follows a group of MI5 rejects who have messed up to such an extent that they have been sent to do admin in the dumping ground of Slough House.

There, they are given their orders by Jackson Lamb, an irascible yet brilliant figure who was once near the top of the service.

Smith came on board the adaptation having been sent the first two of Herron's Slough House books, the only two available at the time, by See-Saw executive producer Jamie Laurenson.

"I'd sent our exec [him] a spec script that was in a similar tonal space," Smith explained. "It was a drama but it had funny moments, and he really liked that. And then I think because of my background working for Armando Iannucci on The Thick of It and Veep, it seemed like I'd be a good fit.

"If you wanted to do a condensed pitch for Slow Horses, you could say it's The Thick of It meets Smiley’s People. I read the books and was just blown away."

You may be wondering why Herron, Smith and See-Saw were having these meetings back in 2014, when the first season was only released eight years later, in 2022. The truth is, that is often the pace at which the TV industry works.

Smith had warned Herron of this, with the latter remembering him saying, "This is all going to go very, very slowly, and then it'll start going incredibly fast."

So it did. For many years, nothing happened, during which time Herron went from writing as a second job to full time, and wrote five additional Slough House novels, bringing the total to seven.

Then, See-Saw happened upon Apple TV+ as a broadcaster. Once that deal was done, producer Graham Yost came on board, and after that, Gary Oldman signed up to play Jackson Lamb.

"Gary was such a coup," Smith says. "He also unlocks all the other cast. So suddenly the whole production just becomes bigger and it becomes, 'Well, if Gary Oldman’s in it, it's got to look amazing, and we've got to have Oscar nominated director of photography Danny Cohen, we've got an amazing director with James Hawes, and then Kristin Scott Thomas will come on board, and Jonathan Pryce will do it,' because it feels much bigger."

With the cast assembled, it was time to get the show on the road. But how would the show be different for fans of the novels, and, crucially, what would Herron think the differences are?

"For me, the biggest difference between the novels and the adaptation is purely the medium," Herron says. "I think that everything that could be done to bring a book onto the screen has been done by [Smith] and the other writers and the producers and designers and everybody involved.

"Obviously, there have to be changes, because most novels, and certainly mine, deal with interiority. You can't go into a character's head - I mean, not without doing voiceover. So, instead of me writing down all the characters' thoughts and feelings, we find different ways to portray them on the screen.

"But it's done with such enormous fidelity to the characters - not to the plots, which is not important to me, but to the characters, which is important to me - that the difference is purely one of transmission. [Smith] totally, as do the other writers, gets the mood and tone of the books."

Herron reveals that, at an event the previous evening, he had read a scene from the script to season 4 episode 1 of Slow Horses, in which Roddy Ho attends a Christmas party, only to realise he's been duped by Jackson Lamb.

"I said, I did not write that scene, but I would have written it, because it’s absolutely in keeping with how I write and how I view these characters," he said. "So it’s absolutely perfect. In terms of the disjunction between what I'm doing and what the writers are doing, there really isn't one."

Smith explains that Herron is always brought into the writers' room at numerous times during the project, and is talked through any changes being made.

"We want to be totally true to the essence of the characters, even when they're cast slightly differently from how they're physically described," Smith says. "Roddy Ho is a good example, because Chris Chung is pretty ripped."

While Herron says he doesn't focus on the characters' physicalities, and doesn't have an image of them in his head while writing (whether as the actors who now play them, or not), he does suggest that Chung is "how Roddy would like to be", and that Roddy himself is "weedier".

"But once we cast Chris, he was so brilliant," Smith says. "And it's such a hard part to cast, to be able to play him without him being completely loathed. He is objectionable, but you sort of forgive him because he's in his own world.

"And once you've got Chris, looking like that, you think, 'Ah, that makes sense.' So you add weights to his office, and then you see him doing a pull-up. You build from the actors. I feel my role is putting your characters through the filter of the actors," as well as to make the show "feel as fun and surprising and as exciting as the books".

What about challenges? Given the success of the novels, that can't be an easy feat, and there is plenty in the stories which is difficult to convey on screen.

"In the season that’s coming up, season 5, the challenge we had was Mick does a brilliant thing at the beginning where there's an attack, and he writes it, and you think you're somewhere in the Middle East, and then you reveal it’s Derbyshire, and that is brilliant," Smith says. "We cannot do that in the show."

Herron says: "That was pretty much just the vocabulary, I just picked words. And I had 'sand-coloured' in the first sentence, so that gives a certain kind of impression for the reader.

"But I have found that in the books that I've written since the show was up and running, I have - it might have been my subconscious at work - I've always included stuff that would be impossible to film."

"Thank you very much," Smith replies with a laugh.

Herron notes that he has never considered screenwriting himself for this reason - he has ultimate flexibility with plots and his imagination, able to write whatever he wants without having to think about logistics or budgets.

"I can spend 10 minutes conjuring up a scene which is going to cost literally hundreds of thousands of pounds," he says. "'Why don’t I have Roddy drive a bus through the front door?' I write it in a sentence, and then it creates a whole situation where everyone’s like, 'We have to buy a bus!'"

However, Smith says he loves this scene, which occurs at the end of season 1.

He says: "That was a very expensive stunt, and what I love about that moment is you do not need it for the story at all. If it didn't happen, it makes no difference, he's too late.

"Ho says, 'I’m taking out bad guys, did I get any?' and Lamb says, 'No we already did that.' It’s a completely pointless scene, but my argument was always, 'You need it for the show.' That won't happen in another show."

Rather than challenges, Smith emphasises that each novel provides specific moments he and the team can't wait to bring to life.

"The big shootout at the underground base at the end of Real Tigers, I thought, 'Oh, great. We get to make the end of a Bond film,'" he says. "And then the attack on Slough House, I thought was such a genius stroke of setting up this precinct where nothing ever happens and then bringing death to the door.

"Then in London Rules, the one that's coming in September, there are several key moments where I was like, 'I’m just so happy we get to do this.'"

Ah, London Rules, Herron's fifth novel and the inspiration for season 5. While Herron says season 4 is currently his favourite run of the show, and is based on his own favourite novel Spook Street, he admits he hasn't seen the fifth run yet.

Smith says he is "really proud of 5", and admits that, when it comes to TV, "each season has to get bigger and better, you can’t go back".

"The most recent one or the one that's about to happen is always my favourite," he explains.

So, what can he tease for season 5?

"Roddy Ho becomes more central," he says, "and it's great to see Chris as he's sort of grown and just owned that character. So that's been wonderful to watch. So it's really exciting to be doing that. And then putting Ho together with characters that might not be able to cope with him, there's real fun to that.

"And then the plot is sadly topical. It comments on contemporary British politics. When [Mick] wrote it, I'm sure [he] thought, 'Oh, that's all going to go away.' But it feels very relevant."

Meanwhile, Herron is also looking to the future of the novel series with his next instalment, Clown Town, releasing in September.

"It's to do with a very horrible, real-life operation that was carried out by the intelligence services during the height of the Troubles," he reveals. "It's set now, it's a Slough House novel, but it's dealing with multiple things that happened 40 years ago and the traumatic and ongoing effects that they have on the people involved.

"And what it must be like for an agent to do something which is nominally for the good in the country and to safeguard the Commonwealth, if you like, but, in fact, is morally dubious and personally traumatic."

Another of Herron's works, Down Cemetery Road, which was released back in 2003, is also now being adapted for Apple TV+. The series will star Emma Thompson and Ruth Wilson, and Herron says it's "looking absolutely tremendous".

That's not all for these two - Smith is working on an adaptation of Andrew O'Hagan's novel Caledonian Road, while there's also the small matter of Slow Horses season 6 beyond that, which will be based for the first time on two of Herron's novels at once, and is being adapted by co-executive producer Gaby Chiappe.

It may have been a slow start for the Slow Horses, but it's fair to say that now it is absolutely full steam ahead.

Mick Herron & Will Smith are appearing at Theakston Old Peculier Crime Writing Festival (17-20 July) at The Old Swan Hotel in Harrogate.

Slow Horses season 5 will start streaming on Apple TV+ from Wednesday 24th September. Seasons 1-4 are available to watch now – sign up to Apple TV+ here.

Check out more of our Drama coverage or visit our TV Guide and Streaming Guide to find out what's on. For more from the biggest stars in TV, listen to The Radio Times Podcast.