They were seemingly successful, and moved to Panama years later where they planned to live out their days together - but a change in visa laws meant they had to fly back to the UK, where John planned on handing himself in, claiming amnesia. The police uncovered the whole story and they were eventually found guilty of fraud and served time in prison.
The story is set around Hartlepool, more specifically Seaton Carew, and anyone with local knowledge (as this Teesside writer with a very loud and proud accent does) will know the accent is not an easy one to replicate. But Marsan, despite hailing from Stepney, London, manages to pick it up quite well.
We decide to get the elephant in the room out of the way first - how did he do it?
"It's the hardest accent I've ever done. It's hard because you don't want to do Geordie and you don't want to do Yorkshire, and there are subtle differences, where different people from different areas of Teesside have different accents, based basically on their class. Me and Monica [Dolan] just kept it going away from scenes so we could sound like a married couple, because married couples tends to have a kind of shorthand.
"I'm a big Tottenham Hotspur supporter," he continues, as I wonder where this is going. "At the time, my driver on the show was a big Spurs supporter, and we'd just fired Jose Mourinho. We were trying to get [Mauricio] Pochettino back as manager and every time, my warm up when I got back into the car to start filming every day, I would say to my driver, [in Hartlepool accent] 'What's happening with Pochettino?' And then I'd be in action all day long."
On to more serious matters, then. The retelling of the Darwin story is complex, mainly as it's retold from the perspective of Anne. While she was found guilty for her part in the crime, her failed defence of ‘marital coercion’ may have been viewed differently in the post-MeToo era.
It's partly this complexity, while balancing the absurd humour of the situation, which drew Marsan to the role - and what surprised him when delving into Anne and John's life a little more.
"I think what was brilliant, and surprised me so much within the writing, was that they loved each other. When I did Tyrannosaur 12 or 13 years ago, when I played an abusive husband, the abuse was so extreme, and it was so far away from the norm it was comfortably away from the norm. It was something that the audience could look at and judge, but it wouldn't challenge them, they wouldn't have to question themselves.
"What's brilliant about The Thief, His Wife and the Canoe, and a lot of dramas post MeToo, is that now the abuse is more nuanced, and it's more subtle. Dramas are now asking us to question ourselves in our relationships you know, they're no longer monsters, they're human beings who are manipulative and abusive in very subtle ways."
It was also the casting of the sublime Monica Dolan ("one of the greats of our generation") that encouraged Marsan to take part. Dolan plays Anne, John's long-suffering wife, and the narrator of this retelling. The on-screen relationship Marsan and Dolan create is frighteningly real - but it wasn't without hard work behind the scenes from the pair.
"Monica and I work in different ways, but we both try to achieve the same thing. She writes reams and reams of stuff - she's got copious amounts of notes. During a scene she'll hide them in drawers! She has this complex narrative that creates which you can see expressed in all the parts she plays. She's an amazing actress like that," Marsan explains, very honestly showing how in awe of Dolan he is.
Marsan's process is different. He records himself and plays his own tapes intertwined with music (ABBA for John Darwin, believe it or not). But there was one element they both agreed on - they wouldn't speak to each other out of accent.
"As soon as we heard we had the same voice coach and as soon as we heard each other speak, we knew the key was to respond to each other in a tone that gave an impression of familiarity. So whenever you'd heard these two people talking, you'd believe that they've lived together for 30 years."
So, The Thief, His Wife and the Canoe has the dedicated cast, the accents, and a talented creative team behind it. With all that in place, was Marsan nervous about taking on a story almost everyone in the UK knows about?
"I did [feel pressure]. But it was alleviated a lot, because a lot of the work had been done by Richard [Laxton, director] and Chris before I came on board. The real challenge of this drama is that it's tragic, it's unbelievable, and it's funny. Some writers and directors find it very hard to write something that incorporates contradictory elements. But great writing always does.
"So by the time I came on, it was already taking shape. It already had all those elements in and it was finely balanced. So all I really had to do was not mess it up. Really I just had to do whatever Chris had written and whatever Richard wanted me to do."
The Thief, His Wife and the Canoe really does balance light and dark. You'd expect from the trailer (and simply just knowing the story) that you'd be in for a comedic romp through one of the most unbelievable true crime stories of the past decade.
What you get, however, is a nuanced tale which yes, addresses the absurdity of the tale, while also exploring the notion of coercive control, grief, lies and ultimately whether a person who's committed a pretty terrible personal crime - lying to her sons - can be forgiven. This is very much a story that centres Anne for the first time.
"It's a story about Anne and her sons and how they forgive her, really. And redemption - she finds redemption. That's what I would like people to come away with," Marsan reasons. "It's not to dismiss what you did, and not to excuse in anyway. But it's a story about forgiveness and she challenges us to forgive, but you can't really challenge people to forgive unless you're really honest about the offence."
After filming this four-part series, delving into the world of John Darwin, and meeting the people of Seaton Carew (many of whom told Marsan they knew John was alive), how does the actor feel about John now?
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Marsan ponders his answer for a moment. "I think he's symptomatic of an aspect of masculinity that our society has created over the last maybe 200/300 years, really, where men have such a fragile, brittle ego that they can't accept their own fallibilities, that they live within this kind of myth of omnipotence and when it's challenged in any way, they can't survive.
"They have to create a fake reality in order to exist, as you can see with politicians in the US election, you see in politicians in this country - you know they're standing at the despatch box lying to us and we know they're lying to us.
"And yet, they live in a world where in order to feel secure within themselves, in order to survive, they have to live in a world where they are the only three-dimensional human beings - everyone else is two-dimensional. They live in a world where they're the centre of the universe, and everybody else is two-dimensional.
"And therefore, 'I can lie. Because you're two-dimensional, and I'm three-dimensional, you don't have the capacity to see the complexities that I'm thinking.' And in reality, you're looking at me thinking, 'Shut up!'"
In my reality, I could listen to Marsan talk for hours. With a part in the new Netflix movie Choose or Die, and a role in an American series he can't talk about yet, plus a growing career behind the scenes writing, it seems the world is about to have a lot more Marsan. And it can't be a bad thing, even if he modestly apologises for appearing on our screens too much.
"No one employs me to be me, you know, they always employ me to be someone else, which I take to be a great compliment as an actor," Marsan levels. "I want to keep doing that, because I'm quite boring. John Darwin is fascinating. Eddie Marsan is boring."
The Thief, His Wife and the Canoe starts tonight at 9pm on 17th April on ITV and ITV Hub. If you’re looking for more to watch, take a look at the rest of our Drama coverage, or check out our TV Guide.
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