Sharon Horgan's diary

I had lunch with Reese Witherspoon a couple of months ago when she was in London. It is amazing how much American writers and producers respond to British comedy. They seem to have a knowledge of even the most obscure shows. Reese had seen

My kids do get some perks out of my job. This summer I took my daughters to South Africa because I was filming The Borrowers with Christopher Eccleston, Stephen Fry, Victoria Wood and Robert Sheehan. I play Homily Clock and Sadhbh, my eldest daughter, had a walk-on part as one of the little Borrowers. She was so thrilled to be in it, but I'm a bit worried that you'll only be able to see part of her ponytail. She was giving it the big 'Suck on this, losers, I'm in a film' to her friends, so fingers crossed she gets her three seconds of screen time.

At the moment I'm at the Menier Chocolate Factory from dawn till dusk rehearsing for the world premiere of Terrible Advice. I'm not used to the enormous amount of preparation that goes into a play. We spent an intense but almost leisurely month in a rehearsal room just pretending and now we're in the theatre for only two days before we open. Suddenly all that luxurious time has turned into a big kick-bollock scramble. It's terrifying, which you don't get with TV or film because you have so many chances to get it right. Unless you're in a soap, when you have to rely on swearing to get a second go at a scene - apparently that's how soap actors get another take; if it's gone badly you just go, 'F*** it!' or 'BALLS!' at the end and then they have to do it over again.

Terrible Advice is written by Saul Rubinek who, among his many and varied roles, played Daphne's lawyer in Frasier. I love Frasier, but it was when I worked out that he'd also played the dickhead producer Lee Donowitz in Tarantino's True Romance that I got all starry eyed and fan-shy. The play is funny and grim in equal measure. It's a four-hander with me, Caroline Quentin, Scott Bakula and Andy Nyman. There's quite a bit of time when I'm not on stage and can watch, and when I do, I'm really laughing but I'm also like, 'Oh God, that's unbearable.' It's about four people making decisions based on their age rather than what they actually want. That question of feeling like you're too old to make any other choices. It's something that I can relate to, when you start obsessing about your 'life diary' and how best to spend your years. Jesus.

The theatre has very kindly given me a room to write in when I'm not needed on stage. Every day Holly Walsh, who is co-writing a new sitcom with me, comes to the theatre and we run upstairs for an hour or two. It started off as a prison comedy (we wanted to call it 'Bitches', like Bad Girls but worse) but it became much more about my character being stuck in prison for something she didn't do, so now there's a murder mystery element, too.

We've found it hard to get into prisons to do research. In fairness, I understand why they would tell us to get lost. 'Hey, we're going to write a silly comedy, can we come in and have a little look around this terrible place where people are confined and their personal freedoms removed? Ha! Brilliant! Thanks very much!' We did write to a women's prison and got a letter back basically saying, 'You're having a laugh,' but not in such a nice way. Instead we've been watching fly-on-the wall documentaries and meeting ex-prisoners because we needed it to be anchored in reality and not just completely ridiculous.

Once rehearsals are over and life returns to normal, I'll be back writing in my office at the bottom of my garden in Hackney. I've lived in Hackney for seven years and I love it more each day. It's a brilliant place to live. So much park life and a great artistic subculture, whatever that means. It's not all riots and gang warfare. There are also some really nice cake shops, and pubs that stay open very, very late. And you can't really ask for more than nice cake and pubs.

Terrible Advice runs until 12 November (020 7378 1713; menierchocolate factory.com)