When a striking image of David Tennant lying bald and incapacitated in a hospital bed began circulating only a matter of weeks ago, the context was unmistakable. He was, for all intents and purposes, Alexander Litvinenko.

Immaculately staged in a near-identical hospital room, the original photo has become synonymous with the 2006 poisoning of the former FSB and KGB agent. It's a murder which saw Litvinenko's tea laced with the rare isotope polonium-210, as he met with business contacts in London's Millennium Hotel.

Sixteen years on, Tennant's goosebump-inducing on-screen performance as the ex-spy sees the actor solemnly announce: "I need to report a murder... mine".

Unequivocally fuelled by justice, long-awaited ITVX drama Litvinenko saw the ex-spy's wife Marina directly involved in the project. Sharing details of her husband's final moments with cast and crew, the series documents events up to the present day.

"I remember it happening," recalls Tennant, 51, best known for his roles in Doctor Who and Bad Omens.

"I remember being appalled and bewildered and shocked and confused by the news story like the rest of the world was.

"With every step along the process, it just felt like a story that had to be told."

The onboarding of Tennant as an executive producer is ultimately what secured the project's viability. Working alongside fellow exec-producer, author and documentary maker Richard Kerbaj, the powerful four-part drama was penned by George Kay (Lupin, Killing Eve) and led by Bafta-nominated director Jim Field Smith (Truth Seekers, Criminal: UK).

Trusted by Litvinenko's surviving wife Marina, Kerbaj had previously documented the family's hard-fought legal battle with the British government. Pushing for an official public inquiry into Alexander Litvinenko's murder, which eventually took place in 2015, Marina says she has fought hard to "keep his voice alive".

"I wasn't sure it was gonna happen. But it happened," nods Marina Litvinenko, 60, of her husband's story being transformed into an ITV drama.

Alexander Litvinenko's killers were eventually named by the government as Andrei Lugovoy and Dmitry Kovtun as part of a 2016 public inquiry. In turn, the historic legal case pushed the British government to admit the Russian State had a hand in the spy's death - noting he was 'probably' murdered on direct orders from Russian President Vladimir Putin.

Claiming political asylum in the UK in 2000 after publicly criticising Putin's regime, Alexander, affectionately known as 'Sasha', foresaw the gravity of his decision.

"Sasha told me, 'Marina [there] is definitely going to be Hollywood movies about our escaping'," smiles the wife of the former spy.

"I said 'Okay' - I was always a little sceptical.

"After his escape from Russia, I was more thinking 'how to live another life, to settle for our son?'. And Sasha was more... just artistic or lyrical."

Stepping into the shoes of Marina Litvinenko is Russian-born actress Margarita Levieva (The Lincoln Lawyer). A connection that almost beggars belief, it later emerged the actress' stepfather was a lawyer who met with the Litvinenko's in Ankara, Turkey, when the family sought asylum in 2000.

"I had a lot of doubts whether I could actually embody her," admits Levieva.

"When I went to make it [the audition tape], something in me came through. And it was something bigger than me, in a way that Marina has told me many times that the need to tell the story is so much bigger than her."

Reflecting on her early years in Russia, the 42-year-old actress says she was "not surprised" by the "devastating" death of Alexander at the hands of the Russian State because she "knew well of the man [Putin] and what he's capable of."

It's a view seconded by co-star Tennant, who adds: "It's also the kind of emotional fracturing of a family."

"That kind of terrible truth of what was attempted by this gangster who happens to have all this power - and how unjust that was and how unfair that was."

"Once you meet Marina, you feel you're not only carrying the importance of this story as a fable for our times, as a signifier for things that the world needs to be alerted to, you're also carrying the story of a family and the story of a couple and that felt very precious and very delicate."

A tale Tennant deems "important on a kind of geopolitical scale", director Jim Field Smith agrees with the Doctor Who star, noting the story is fundamentally "about bullying".

Recounting the call announcing the project had been given the green light, Smith describes a serendipitous moment which saw him standing in London's Grosvenor Square as he received the news.

"George [Kay] had called me about it. I was listening to an audio version of a Guardian article about the case and I actually walked into the lobby of the Millennium Hotel listening to the podcast," admits Smith.

"It was really strange to sit in the Millennium Hotel and feel the ghosts and characters of the story around me."

Describing how the tale unfolds across four distinctive episodes, he says the final instalment is "almost exclusively" concerned with Marina's fight for justice.

"Unfortunately, as much as there are bullies in Russia, they're also bullies in this country as well. And the British government felt unable, at times, to allow the inquiring inquest to go ahead, because they felt like there were bigger interests at play, let's just say," says the director.

It's a view shared by Marina Litvinenko, who puts it simply when she says: "I just started to realise: everybody has their own agenda."

Describing the way in which the British government "could no longer ignore" what Smith describes as the "absolutely obvious truth", the director sums up his position with a shrug.

"And here we are now... he's, rather foolishly some may say, invaded Ukraine - and got slightly more than he bargained for."

Litvinenko airs on ITVX on Thursday.