In the forthcoming BBC comedy series Can You Keep A Secret? Dawn French plays Debbie Fendon a ‘tinpot dictator’ who maintains the illusion that her husband William (Mark Heap) is dead, hiding him away in the loft for a few months until the life insurance pays out. The cast also features Craig Roberts as the couple’s son Harry, and  Mandip Gill as his wife Neha. Here French talks about the role – and, below, Mark Heap adds his thoughts…

Why did you say yes to this role?

It's an interesting hybrid, and I think that's one of the things that attracted me to it because it is a sitcom, without a doubt, but it's also a thriller, and I think it’s quite hard to pull both those things off. It’s funny, but it’s also about the dynamics of this oddball family that have Almost Accidentally pulled off a massive crime.

William, played by Mark Heap, is very poorly with Parkinson’s, and he’s been shafted by health insurance companies. So when this opportunity arises for my character Debbie to fake her husband’s death and claim William’s life insurance, I don't think she has any qualms about going ahead and committing the crime. She thinks it's justice and she feels righteous about it.

Can you tell us a bit more about Debbie?

Right from the off I could see that she's one of those people who absolutely believes she's always right. 

I don’t think I’ve ever done that in my life, been sat firmly in that righteous place the way Debbie is. I may have often imagined that I could be right, but I’ll err on the side of thinking, ‘I'm probably wrong about this’. Debbie just doesn't have that anxiety or filter. She’s made a split decision in a mad moment, and once the decision is made, unless she’s prepared to go to prison, she knows she’d better man up and deal with it. 

I mean, I've never been in this situation, but I guess once you make a life-changing decision like that, and you jump into the dilemma of it, you've got to gird your loins and get on with it because once you’re in, you’re in.

She’s not always likeable, but did you like her?

She’s not a bad person; she's a bossy person, and she's determined that this will work, and so she has to lead the cavalry and she minimises a crime.

It’s terrible that she does that, and she puts the whole family into a moral dilemma, and the whole thing is her idea and her fault, and she's prepared to go a long way, and she's prepared to betray her friends and do a lot of things that aren't very likeable, and she’s manipulative. But that said, she’s quite real, and it’s a real dilemma that makes me think, ‘What would I do?’.

Without getting too Method about it, I did have to try and think like her. I had to think, why is she doing this? From that Sliding Doors moment that’s offered to her, it’s impossible to stop. She didn’t plan this at all. 

Everybody thinks William is dead, and he doesn’t go out much anyway, so it’s not going to be too difficult to keep him indoors. They’re both angry because they haven’t been able to claim on their medical insurance. And putting that together, this stupid, mad idea becomes feasible in her head. It’s a split decision and on she goes: she puts blinkers on and just marches forward.

What’s her marriage to William like?

She’s honest and sometimes a bit brutal with him, but I could also see from the script that the marriage has been going for a long time, so it can withstand that. She might have misjudged it occasionally, but you can see the marriage can withstand this robust banter that goes on. After all, she’s doing all of this for William, and for their son Harold.

Did you enjoy shooting this series?

At the very beginning I said to Simon [Mayhew-Archer, the writer], ‘I'll happily do a sitcom, but we need to set it down here near where I live’, partly because I want to bring more work down to Cornwall, and partly because that puts me close to my family and other logistics. Simon completely agreed to this, but of course, Simon’s not in a position to agree! But we ended up doing it near Bristol which has all the studios and stuff.

That meant most of us were away from home and, when you’re working away from home, the cast and crew become your new family. This is your new gang. That's where you get your laughs and that's who you moan to, and who you cling to. 

When you’re away, it helps when it's a happy gang. And it was a particularly lovely gang, from the camera crew to the sound guys to the drivers. Everyone was up for it. Even the guys who were doing the catering said the story sounded intriguing. It didn’t feel like we were on any old job, doing any old thing, and that’s everything.

I think that's the other thing about this: it was a younger writer, a younger director, younger producers, people that were prepared to make a gang without having hierarchy, and they were listening, and their collaboration was good.

Did you enjoy specifically working opposite Mark Heap?

So much. I had a little worry that we'd already worked together on Whatever Happened to Maggie Cole? [the 2020 ITV comedy-drama], and the legacy of that might be a hurdle for this. I didn't want people thinking about that when they're watching this, but the desire to do this job trumped my worry about that. 

[Mark] is a wonderful human. I don't see him all the time or anything like that, but we bob each other a couple of texts every now and again, and there's instant love whenever we're together, and massive support. That's what you need on set. He's a proper mensch.

And the rest of the cast?

Really, it’s an ensemble piece. For all that there are four of us at the centre, there’s an entire gang around us who provide lots of hilarious comedy like Geraldine McNulty and Paul Chahidi. But all of them in that little gang matter very much to this story and are key because we need to know who’s blackmailing Debbie, and so we’re looking at everybody. Simon’s written a good ensemble of characters.

Interview with Mark Heap  

Tell us about your character?

He's a loner. He's someone who is quite happy in his own company, as am I. There's a good line where Debbie says ‘no one would notice you're dead anyway, because you don't go out, you just sit around upstairs’. So there's a bit of that going on, I think.

What is Debbie and William’s relationship like?

Like a comfortable old sock that you put on or a jumper. They've been together for a long time. There's a little bit sometimes zoning in and out of each other's thoughts or words. She's quite bossy, Debbie, but I don't mind being bossed around. We're still very much in love, I think, in our own peculiar way, as is with a lot of couples who've been together for a long time. 

What has been your favourite moment to film?

Watching my fellow actor Mandip struggling to watch me vomiting. Watching her retching, genuinely. So that was quite good. I don't mean to be cruel, it's quite funny.

What would you do if you were in William’s situation?

I wouldn't have any trouble at all hiding away for months and months. I've got my inner voices to hear, and I've got thoughts to think, and sights to see, and sounds to hear. I think that's all the senses. Feelings to feel, there's another one.

Who is the best bluffer on the show?

The writer, Simon Mayhew-Archer. He pulled a trick on me. I like to know my lines well in advance, and he approached me with a new scene to be done the following day, which involved a long speech and Welsh and all kinds of things. He played it really well, and my reaction was exactly as expected, like, ‘I'm not doing that!’. And they went, ‘Oh, no, we're only joking’. So, yeah, he was very good.

» Interview with Can You Keep A Secret? writer Simon Mayhew-Archer 

• Can You Keep A Secret? is on BBC One and iPlayer from 9.30pm on Wednesday January 7.