Stephen Mangan, 56, was born in Enfield to Irish parents. He studied law at Cambridge but took a year out to care for his mother, who died of colon cancer aged 45. Weeks after her death, he successfully auditioned for Rada and went on to become a stage actor. His TV breakthrough came in Adrian Mole: The Cappuccino Years. He has since starred in Green Wing, Episodes and The Split. He co-hosts Landscape and Portrait Artist of the Year on Sky Arts, and a weekly show on Classic FM. He is currently appearing in throuple comedy Unicorn in the West End and is the author of six bestselling children’s books. His seventh is out in May.

Your sister Anita illustrates your books. What’s it like working with a sibling?
Great fun. Essentially we’re trying to make each other laugh, like we have done since childhood. But because I’m her annoying older brother, I deliberately put things in the book that are difficult to draw.

Do you use your three sons as a focus group?
I use my 14-year-old as a plot consultant. If I’ve painted myself into a corner, I’ll have a chat with Frank. He’s very good at talking me through my logical inconsistencies. Then Jack, who’s now nine, reads a draft while I try not to be the person going: “What were you laughing at there? Why aren’t you laughing at this bit?”

What things do you need to write?
A lot of food and coffee. I come up to my office with a tray full of coffee, nuts and apples. Then I try not to stare out of the window, while eating like a demented squirrel. Acting is a team sport whereas writing is solitary, so it’s nice to yo-yo between the two.

You’re approaching the end of your West End run in Mike Bartlett’s Unicorn. Have you enjoyed it?
I’ve loved it. It’s a play full of good ideas and great lines. Also Erin [Doherty] and Nicola [Walker, his co-stars] are two of the very best. They’re both so present on stage. Sometimes you work with actors who’ve worked out their performance in their bathroom at home and are going to give that performance come hell or high water. What’s lovely is that we all listen to one another and every night is genuinely very different. It’s great that a new play has done so well in the West End. And it feels absolutely contemporary.

What’s been the audience reaction? Has it started conversations or inspired any “throuples”?
We do get standing ovations at the end but we also get people leaving after 10 minutes because they weren’t expecting that nice couple from The Split to be telling each other what they want to do in bed. I know people who’ve had uncomfortable taxi rides home afterwards. We’ve had throuples come to talk to us at the stage door. The other day, we had a bloke and two women who’d been together for 40 years. We’ve had three women who’d been together 20 years. In a way, I’ve got more questions for them than they have for me. You just want to know how it works. Even sleeping arrangements. With three people in a bed, who goes in the middle? What happens if you have to get up to go to the loo?

Have you seen Erin Doherty in Adolescence?
I’ve put it off because we’re doing this play together and it would feel weird. As soon as Unicorn’s run finishes this week, I’ll sit down and watch it. Partly because Erin’s in it and Stephen Graham, who’s fantastic. But also because I’ve got three boys and I think it’s an important thing to watch.

Who do you get more recognised as nowadays – Dan Moody from I’m Alan Partridge or Guy Secretan from Green Wing?
I still get “Dan!” shouted at me several times per week. It tends to be Guy if I go near a hospital. Suddenly a lot of doctors emerge, wanting to tell me that he’s a hero to them, especially if they’re an anaesthetist. Which I’m not sure is terribly reassuring to hear [laughs].

What’s your dream role?
I’ve been playing quite nice people or bumbling idiots lately, so I’d like to play someone really unpleasant. It’s always fun to exercise those bits of you.

Would you like to play an Irish character?
Yeah, I mean for goodness sake! Here I am, Mr Irish – even if I don’t look it. People think I’m a posh English boy, which in some ways I am. I had a posh English upbringing but my family background is entirely Irish. My mum was flame-haired, freckled Mary Donohoe.

Your wife, Louise Delamere, is also an actor. How would you feel if your sons wanted to act professionally?
Well, it’s given me a fantastic life. I’m forever grateful that I decided not to be a lawyer and became an actor instead. Why wouldn’t I want that for my children? Although of course you’re aware of how precarious it is and how buffeted by the winds of fortune you can be.

How do you relax when you’re not working?
I’ve had a Spurs season ticket since 1997. It’s been hellish this season. It’s like going to a huge group therapy session, where 60,000 people sit in a circle and try to examine what’s gone wrong in their life to bring them to this point. And I’m a big runner. A two-hour run is my meditation. I’m doing the London Marathon this week.

What cultural things have you enjoyed recently?
Like everyone else, I watched The White Lotus. My son saw A Complete Unknown and has become obsessed with Bob Dylan, so we’ve been ploughing through all the various Dylan documentaries. I listen to a lot of history podcasts and just read Helen Castor’s book on Richard II. In terms of fiction, I loved The Bee Sting by Paul Murray, Glorious Exploits by Ferdia Lennon and The Ministry of Time by Kaliane Bradley.

You play piano and were in a prog rock band at school. Do you secretly dream of rock stardom?
I think all actors want to be rock stars. But the great thing about acting is you can still do it when you’re 80 and no one goes: “Why is he still doing that?”

• The Fart That Saved the Universe by Stephen Mangan, illustrated by Anita Mangan, is out on 8 May (Scholastic, £7.99). To support the Guardian and Observer order your copy at guardianbookshop.com. Delivery charges may apply