Litvinenko tells the true story about former KGB operative fatally poisoned in London

David Tennant is a man in demand.

The actor can currently be seen in the third season of Staged on BBC One; he’s also the narrator of the channel’s natural history series Spy in the Ocean. He also pops up on BBC Two on Wednesday in the return of There She Goes. Plus, over the coming weeks and months, he’ll reprise his role in Good Omens (alongside Staged’s Michael Sheen) and, of course, will star in the 60th anniversary Doctor Who specials.

From that list you can tell he has the pick of the top scripts around, which is why, when he turns up in a new programme, you know it must be very special indeed.

So, unless you caught the five-part drama Litvinenko on the ITVX streaming service late last year, you should tune into it on ITV1 when it airs across the week. The real-life story has been told brilliantly by scriptwriter George Kay. It’s also one of those times when fact seems stranger than fiction.

For the uninitiated, it focuses on Alexander ‘Sasha’ Litvinenko, a former KGB operative fatally poisoned in plain sight in central London in 2006. The opening episode details his efforts to provide the police with enough information to find his killers before his inevitable death; the rest of the run focuses on the investigation and the revelations that surface during it.

“Like everyone, I remember seeing that image of Litvinenko in the hospital bed,” says Tennant. “It all felt so implausible at first, like something from a James Bond film.

“He should have, as was intended, just slipped away as an unexplained death and we would not be any the wiser. But that in itself then creates bigger questions. You think, ‘How many times has this happened and it’s remained undiscovered?’

“There is so much about this story that is fantastical, implausible and remarkable. And, of course, it’s all anchored to what becomes a very personal story about Sasha, his wife Marina and son Anatoly, which is what makes it so tragic.”

The supporting cast includes Mark Bonnar and Neil Maskell as the investigating officers, with Margarita Levieva as Litvinenko’s wife, who fought for the British government to reveal the names of her husband’s killers, while Jim Field Smith, whose CV includes the second season of Episodes, is the director – he and McKay are old schoolfriends who run the company Idiotlamp Productions.

“There was an enthusiasm from everyone involved in the production at every level that they were telling an important story and that we were doing good work,” says Tennant while explaining his involvement in the project. “That was throughout the production at every level, in every department. It really felt like people were proud to be there. There was a determination to get it right.

“One can’t second guess how this will be received or what kind of impact it will have. But on a purely personal level it’s something I’m very proud to have done. I feel like we gave it our best shot and we are, hopefully, honouring the memory of Sasha and the life’s work of Marina. That’s what we set out to do.”