When I was six, my best friend Isabella and I would make up plays which we would then perform to her poor mother. They were so abysmal I didn’t go back to playwriting for 20 years. I acted in a couple of plays at school, then studied Philosophy and English at St Andrews, got involved in the drama society and started directing. I’m not a very good director, but I loved working with actors and on the text.

I did an MA in Text and Performance at King’s College and RADA, and wrote my first play, The Soldier. After it went to the Edinburgh Festival, I was approached by an agent and got a job writing for an appalling programme called Dream Team – one of the worst dramas I’ve ever seen. I lasted about four months before being sacked. I was scared of the producer, the producer hated me – it wasn’t a happy marriage, but by then I’d had a paid writing job, so I knew it was possible. I’m not from a theatre background – my dad drives buses, my mum works in a primary school, so this was not only an alien world to me, but once you’re there, there’s no way out. It went from there.

I first approached Sebastian Faulks about Birdsong in 2006. He said he thought Working Title owned the stage rights, but asked me to check with his agent. I never expected to hear from him again, but I had an email back and then a meeting. I took a treatment of how I would adapt it and said I would be faithful to the spirit of the book but would elide characters and events where necessary.

It was a very slow process – every time I wrote a draft I’d send it to him and he’d give me notes. He was always very complimentary and encouraging. On the first draft, he said I’d captured the spirit of it and had the voices and rhythms of the characters, but there was too much swearing and too much singing! I’ve moved some events around to build the drama. For instance, Stephen and Isabelle’s reunion happens much closer towards the end of the play than the book.

Sebastian is a kind and gracious man. He says, “This is your play, you make the choices you need to and if I really disagree, I’ll let you know”. I’ve also adapted his novel The Girl at the Lion D’Or for radio, so I hope there’s a lovely working relationship there which we can continue to build upon. I tease him and say, “Please write more books, I need to adapt them!” Sebastian spent 13 years watching the film floundering in development hell, so he found theatre delightful in comparison. I wanted him to believe in it fully, which he seems to – he’s seen it six times!

I’m currently writing a play about Cy Grant, a Guyanese man who was one of the first black men in the RAF. He flew various missions before his plane was shot down. He ended up in Stalag Luft III for three years. After the war he came to the UK and couldn’t find a job becuse of the colour of his skin.

I’m fascinated with how we behave as human beings. My friends are under the illusion I work incredibly hard but there’s always washing to be done, the dog to be walked or some cakes to be baked urgently. I also like to go away – Mike Bartlett and I often go to St Andrews for a week in the summer, rent a cottage, write all day, cook a nice meal and sit by the fire, watching The West Wing. Once he made me watch Doctor Who. I have almost forgiven him.

Rachel Wagstaff was talking to Miriam Zendle.

Birdsong is at the Comedy Theatre, London, until 15 January.