Litvinenko is a "feat of acting" from David Tennant, says Neil Maskell

"I'm very nervous of saying anything that might be disrespectful of the realities of the actual situation in that room in 2006," said Maskell, who plays DI Brent Hyatt – a police detective tasked with interviewing the dying Litvinenko – in the series. "But it affected me in two ways, really.

"As an actor, a big part of your job is, very early on, you set the parameters that you're going to play the part in, right? For instance, if you're playing Doctor Who, the parameters are quite broad – you can go quite small, or things can be f**king wild. So you've got loads of room, it's a dance, and you can do what you want – and if you're really mustard like David Tennant is, or Jodie [Whittaker] who's just done it, you can dance inside all of that.

"Really, that's the widest parameters you're gonna get and other than that, as you're working, you're always working inside different parameters that you set in terms of the character's volatility, or how mercurial they are, how they might skip through emotions or whatever..."

Maskell explained that he was left stunned by Tennant's ability to convey so much in his performance despite the majority of his scenes taking place with an ailing Litvinenko confined to his hospital bed.

"He's in bed, he's laying still. He is modulating the very slow progression of a poison working its way through his body until he dies... and he's fighting that as an incredibly fit man – Sasha Litvinenko ran 10k a night, otherwise he'd have been dead within hours.

"To see him [Tennant] find dynamic and modulation across those scenes, the feat of acting, without moving, and to mark the deterioration and to hold on to, for instance, the very technical thing of hitting cues and delivering lines and having big chunks of dialogue that you can't just put loads of big gaps in and let the scene die...

"To watch him do that as an actor in the same room – and for him and Margarita [Levieva, playing Litvinenko's wife Marina] to be in such synthesis and there to be such truth in a relationship between them and her responses to his deterioration...

"It was just... Actors always go on about how much of an honour it is to work with people and whatever, but genuinely that was something to see, up close, for however many days it was – five or six days."

Maskell even described the scenes in which DI Brent Hyatt interviews the dying Litvinenko as "the most powerful and connected of my career".

"Once you're older than 30, who hasn't sat next to a hospital bed while someone's gone?" he elaborated. "We've been there, unfortunately a few times and I'm sure a few times more [to come], so the emotion, with the noise of the machines, with knowing the weight of responsibility we had of the story, of David and Margarita's performance, and of my own experiences of that exact atmosphere and environment, they're the most powerful and connected [scenes] of my career, actually.

"Jim [Field Smith] tried to keep the crew outside [the hospital room] and it was just us in there with a camera, but you could feel it off the camera operator and the focus puller, this kind of fizz. It was very powerful."

Read more:

• Litvinenko director: Nailing David Tennant's Russian accent was "tricky"
• Litvinenko writer explains change of lead actor and genre each episode
• David Tennant explains how he transformed into Litvinenko for drama
• David Tennant: "Intense" Litvinenko was "a story that had to be told"
• Litvinenko’s widow Marina reveals why she agreed to ITVX drama
• How David Tennant "saved" Litvinenko when ITVX drama was under threat

Litvinenko arrives on ITVX as a full boxset on Thursday 15th December.

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