Was there any extra research you had to do around the political world of Westminster for this book?

Yes, you’ve got this amazing building that’s been the seat of power in the UK for hundreds of years, so it was essential for us that it felt realistic. In order to make that possible, a lot of us Heads of Department went on very specific tours of the Houses of Parliament. There are superb tours where you’re brought through all of the Chambers, I think a two-hour tour. So, it was great for us to see the real thing.

They don't grant permission to film in the Houses of Parliament, so we needed to replicate it, which meant getting our heads around what happens there and how decisions are made. It's also really interesting to see what the back offices look like. There’s a whole process in terms of how you’re introduced to the space.

It was important to capture that accurately. In this series, we follow Robin as she goes undercover in Parliament under the guise of being a researcher called Venetia. There’s all the trepidation that goes with entering a building like that, not least undercover. And it gets less and less glamorous the farther back you go. The offices are a little bit shabby, people are just getting on with their business, and it's all quite normal. But the initial approach is quite intimidating.

Were there any particular challenges with this book in terms of specific locations or scenes?

There are new and different challenges with every book, each presenting its own set of locations, stunts, and chases. We had an interesting couple of nights doing one particular sequence in which Robin is supposed to fall into this deep dell. And there’s a set-piece where Robin and Strike are chased by vicious dogs. They’re stuck in this barn building, surrounded by these dogs, and they need to figure a way out. That was a bit of a challenge.

We also did an exciting chase sequence at Flick’s flat, after the party scene there. It's the moment when Jimmy cottons on to who Robin is. When we scoped out the location on the recce, Sue choreographed the entire chase sequence with great detail. It’s a big, sprawling estate with lots of levels, so the tension builds during the chase until it culminates in this archway with Jimmy being run down by police cars. It was technically quite a tricky stunt, but it really came together on the night, precisely how Sue had planned it.

Those were the usual challenges. The other challenge is keeping everybody happy on the road, sometimes under the less-than-hospitable winter conditions.

You filmed in quite a few big stately homes, can you talk about what they were used for?

Yes, the scale of locations on this one has been pretty significant. In other books we’ve more or less tended to end up in and around London, with the odd trip to Yorkshire. But this one took us on a whistle-stop tour! We had 53 locations to shoot over 60 days, so the schedule was pretty intense. It meant that sometimes we’d be in a location for a day, pack up and be on to the next one that evening. And with that number of locations, finding the right ones was its own challenge.

Chiswell’s country house, for example, had to be a grand, old and crumbling estate in the middle of the countryside. The family can’t afford to keep it maintained, so we needed to find something that had the right balance of opulence and decay. It also needed to be somewhere Kinvara would plausibly have stables for her horses.

Finding that within the M25 was a challenge, and we couldn’t find something of the appropriate scale. Various properties offered different things, but eventually, the locations department found Dinton House outside Salisbury, and that ticked all the boxes for us. Plus, there was the perfect dell nearby that we also needed, so we were very happy there.

It’s vast, in precisely the way we needed. We were able to get some great drone shots over it. We needed to capture the sense of this being Chiswell’s country home, whereas in the city, we see him in a smaller, albeit very fine, townhouse. The other thing that proved a challenge, which is always the case with the Strike books, is the level of research: with many of the locations mentioned in the text, you just know she’s been there. The White Horse pub, that’s namechecked, as well as Pratt’s Club and Le Manoir. We were very lucky to be able to film in those locations. It’s a real privilege. Not many people will get a glimpse of Pratt’s! You can feel the history in a place like that, and I think the cast enjoyed being in the authentic location. It felt like a real coup.

Our supervising location manager is the first person to make these approaches. Because the book had been out for about a year before we were due to start filming, some of the establishments were namechecked and already aware of their being featured in the novels. They’re very proud to be part of it, so they often generously open their doors to us.

It was quite amusing with Pratt’s though, as they were aware of the book, and were growing used to fans knocking on the door, trying to get in. So the deal with them was that, although we could film there, we could only show the interior and not a shot of the exterior door, because they’d had enough of fans trying to get a peek!

Lethal White brings us back to Strike’s world in London. Can you talk about the role that London plays in shooting the series?

London itself is such an essential character in this series. From the very start it’s been vital that we show it as it is. And that’s something we hear from viewers, that London feels like a protagonist of its own.

In Lethal White we return to Strike’s offices on Denmark Street, which is its own challenge, because there’s so much construction going on in advance of the Crossrail. So one side of Denmark Street is now surrounded by scaffolding, while the other side is still intact.

We’re crossing our fingers and toes that it will remain so for the next couple of years. It’s Strike’s home. He belongs there, and its hard to imagine him working or living anywhere else. Interestingly,he’s never moved out of that bedsit, even though, a year on, he probably could, as business is ticking along and he’d have a bit more money. But I don’t think he could conceive of living anywhere else. Being above the guitar shop, it’s almost a nod to his parents - his mother, the groupie; his father, the rockstar. It’s wrapped up in all of those things.

Beyond that, the texture and colour and feel of Soho are all so crucial to the show. Yes, people will tell you how much Soho’s changed over the years, but it still has that character. The grittiness. A certain realness. It’s a joy to capture on screen.

The Land Rover also features again in this series. Can you tell us about how it’s used?

The Land Rover is another character in itself. It’s fought for and earned its right to be described as such, four books in. It’s one of those places where we can put Strike and Robin into a confined area and basically force them to communicate. It also represents access to the wider world, a chance to get out of London, to head into bigger spaces in the countryside.

Sometimes it’s a space for them to think, to figure out some remaining clues, so it also becomes a useful space. As well as a place where they share some banter. It also gives us some lovely, revealing, personal moments - like Robin feeding Strike biscuits. How they relate to the car is revealing in its own way. Strike’s always looking for food and rummaging around for things. For Robin, the Land Rover might represent aspects of her past: growing up in Yorkshire, for example, or having a pony. I think it’s quite a safe space for her.

I’m especially thrilled for Holliday because she took that Land Rover like she’d been driving it her whole life. It’s a tricky old machine too, it doesn’t always behave as it should. But they seem to have an excellent working relationship because whenever Holliday gets into the driver’s seat, it transforms into quite an obedient machine. Even our stunt driver doesn’t drive it as well as Holliday!

Can you talk about the London protest scene?

Each of the Strike novels brings us into different worlds. With Cuckoo’s Calling, we had the worlds of Mayfair and fashion models. The Silkworm took us into the literary world, while Career Of Evil seemed to take us deeper into Strike’s and Robin’s pasts. Lethal White draws us into the political sphere. I think we all felt that it was a particularly interesting time to have a Minister as one of our lead characters, because some of the things happening in the book seemed to be playing out in real life while we were filming.

We had a protest scene that we shot around Pall Mall. In the show, an activist group has taken over a public square, and they’re making as much noise and causing as much disruption as possible. Meanwhile, literally 10 minutes up the road, Extinction Rebellion was in Trafalgar Square. We even had a couple of visitors from their protest merging into ours! So there was a certain sense of life imitating art.

Can you talk about how you’ve dealt with having so many characters that are important to the plot in this series?

There are many strands to this particular story, and the plot’s pretty complex. We’ve got the political world of Westminster, the Chiswell family, a left-wing activist group, plus we’re dealing with Jimmy and his brother Billy, which harks back to a secretive past, as Billy thinks he’s witnessed a murder.

Inevitably, when Strike starts digging around, he and Robin come into contact with a wide array of people. This gave us a rich cast of characters and the challenge of casting them. Making them distinct and authentic is essential, and I think we’ve done that. We’ve got a terrific, multilayered cast, and even people who come in to just do a couple of scenes in one day, they’ve all seamlessly fitted into the ensemble.