Stripped away is the star’s usual charisma and swagger, instead replaced with a heavy sense of burden, both physical and psychological.

It’s a steely, restrained performance, reminding us not only that Alexander (or Sasha as he was often called) was a fully rounded human being, at this time suffering from the most horrific attack, but also of his bravery in the face of death, and determination to tell his story.

It’s not particularly a spoiler to say that Tennant’s character doesn’t survive for long. Not only has it been included in ITV’s marketing materials for the show, but it’s also established fact and well-known recent British history. There’s no hiding from it.

One of the testing points for Litvinenko will therefore be how audiences react to the actor’s departure, after which the series takes on a rolling cavalcade of different lead actors, each bringing their own flavour to proceedings. This is, in theory, an experimental approach, but it doesn’t feel as innovative as it perhaps could have done.

The best episode of the series, by some way, is the third, which takes on the form of a Cold War-style thriller and sees a group of police officers, led by Sam Troughton’s Brian Tarpey, heading to Moscow to investigate.

There are a number of reasons for the success of this sequence – Troughton and his co-stars Barry Sloane and Sam Marks are impeccable, Jim Field Smith’s direction makes the sequences surprisingly high octane and George Kay’s script is laced with dread. However, the most fundamental reason is that the history is so compelling.

It’s a point which recurs throughout Litvinenko. Kay noted, when speaking with RadioTimes.com recently, that little fictionalisation was needed when it came to dramatising this story, because the real history was already the most fascinating version of events you could tell.

This is undoubtedly true, but it does mean that across four hours Kay and the rest of the team are at the whims of the true story’s pace, its investigative dead ends, its recurring set-backs. It can make the series feel unbalanced.

The series probably isn’t helped by having the excellent BBC drama The Salisbury Poisonings in its rear view mirror. That series similarly looked at a poisoning on British soil which has been linked with the Russian state, but did so through a profoundly domestic viewpoint.

That’s not to say this series is incomparably weaker – it’s not – it just perhaps feels a bit more rote in parts, and lacking a distinctive angle on events. Another problem is the series’ ending. There is no satisfying conclusion to these events – we know that from the reality of what has happened since.

Unfortunately this does make episode 4, which dramatises Marina Litvinenko’s years-long legal battle for justice, the weakest of the bunch. It’s unsurprising given the dramatic shift in pacing from the jumpy, paranoia-infused third episode to this much slower-paced affair, but a shame given Margarita Levieva’s stellar work as Marina.

ITV Studios for ITVX

Levieva and Neil Maskell are particular highlights from the cast, with both bringing real depth to their roles as the grieving widow and empathetic police officer – these could be one-note parts, but both infuse them with fallibility, pathos, and above all, sheer likability.

It’s where the show leans into the emotional core of those affected by this awful crime that episodes 2 and 4, the lesser chapters, shine brightest, rather than in their more traditional police procedural or court room trappings.

I have no doubt viewers will binge their way through Litvinenko and not come away unsatisfied. It is, after all, a competently-made, true-to-life depiction of events, in a style which won’t be off-putting to viewers accustomed to ITV’s usual drama output.

It’s just also a show which comes burdened with weighty expectations. It stars David Tennant. It’s one of the most highly anticipated originals to be coming out of ITV’s new streaming push with ITVX. It’s telling a well-known yet shocking true story, one which has taken on a devastating timeliness this year.

All of this means that Litvinenko’s more traditional trappings (and lack of Tennant screen-time) might come as a surprise to some. But for those who are able to get their expectations in check, it is still a well-crafted, engaging drama with some impressive performances and an important role to play in helping us remember and acknowledge this barbaric crime.

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

For more news, interviews and features, visit our Drama hub, or find something to watch now with our TV Guide and Streaming Guide.

The latest issue of Radio Times magazine is on sale now – subscribe now. For more from the biggest stars in TV, listen to the Radio Times View From My Sofa podcast.

---