Hit sitcom Ghosts returns for its fourth series on Friday, September 29, BBC One, 8.50pm. There is also a new podcast, Inside...Ghosts, available on BBC Sounds. Details here.

What has made Ghosts such a hit, do you think? 

For a start, the writing is really good. Also, the ghosts and Kiell are so talented and funny and smart - everyone brings their own unique thing to the show. And it's ultimately very, very full of heart. The place it comes from is really loving, and people can feel that. Everyone I speak to says it makes them feel really warm. What more could you want?

Perhaps particularly in difficult times people, love that sense of warmth that it generates, don’t they?

Yes. Without getting too hippie-dippie about it, there's definitely a real sense of community breakdown at the moment. And so to watch a dysfunctional community function in the way that their household does is really heartening. The idea that such different people have to live together and make it work is on some level very profound. It's important that we try and get our society to be like that.

What's going on with Alison in this series? 

The ghosts are driving her crazy! As usual, she’s losing the plot because she's got to deal with essentially grown-up children who are stuck in a time warp and also a leaking house and a very sweet husband, to be fair, who's endlessly supportive and also slightly impractical. She's also a bit nervy and has got high expectations for their new guest house, so she's her own worst enemy. She’s constantly frantically trying to make everyone have a nice time. Nothing like me, who is chilled and aloof and doesn't care!

People love Alison. Why do you think that people are so drawn to her?

The reason I like her is because she's ultimately very warm and she's very optimistic. She really does try to make the best of things all the time, and I think that's a lovely quality in a person. Also, she's never afraid to say how she feels, which I think is really cool. There's a freedom there with the ghosts. But what really touches me about that is that she's so much fonder of the ghosts that she would ever admit. I love that because there's an undertone of real love that is completely reluctant because they drive her up the wall and make things so difficult for Mike, too. Imagine! He's the most patient man. He’s so long-suffering. It's just crazy. It is so lonely for him. That relationship really stands the test of time.

How does Alison and Mike's relationship evolve in this series?  

Alison and Mike are tested in this series. They do row and get on each other's nerves a bit. But they're still very, very strong as a couple. They are trying to make a bit of time for each other. Mike very sweetly in one episode tries to get Alison to relax. He's so caring, and that's really lovely. I love it when you get to see them unite. That’s very sweet. Especially as Alison does not have a family, it really means a lot for her to have him as a support.

What do you hope that viewers will take away at the end of this series?

It shows that the ability to see the humour in things is essential. It manages to pepper a very silly comedy with pathos. Of course, there's nothing funny about death or the reality of our very short lifespans. But what's wonderful about Ghosts is that there's so much humour in it. Anything that can encourage people to lean into that is a good thing. Because humour is the quality that helps get everybody through all this terrible stuff we have to endure. 

Finally, another reason for the show's success is that it has a very broad family appeal, doesn't it?

Absolutely. And that's been something that people overwhelmingly do say to me. They tell me that they love the fact they can watch it with their kids. They are delighted to have something they can watch all together that isn't algorithmically pointed towards their generation. That is really nice. There is also just the satisfying thing of watching with a 10-year-old when the 10-year-old doesn't know why Julian has got no trousers on. My nieces asked me that question. I said: “That’s one for your parents, I think!

Interview supplied by BBC