I saw The 39 Steps before I joined the cast, watching from backstage, which was bonkers. All you could see was people rushing around, on and off stage all the time. Everybody has their own particular ritual off stage, taking a breath and then running back on. The water breaks are really important because there are only a couple of chances to have a drink.

Now that I’m in it, The 39 Steps is turning out to be one of my favourite jobs. When you come on at the end for the bows, you look around to see where everyone else is. I get so used to meeting various characters on Hannay’s journey that part of me forgets there’s actually only four of us on stage. Before this, I was at the Haymarket in The Country Wife, which was a huge, mammoth affair with a massive cast. You’d come on for your scene and then you’d wait and wait and have to psyche yourself back up to finally go back on.

With The 39 Steps, Josefina Gabrielle says it’s like four water slides - you all get on the slide at the beginning and sort of fly down and you end up in a big pile at the end, all together. It’s exhausting but exhilarating. And the audience is like the missing member of the company. It’s different each night. Sometimes they just want to have fun from the very beginning and you can’t stop them laughing.

As Hannay, I’m in the same costume the whole time, whereas the other cast members have to do all these mad changes. The only reason I envy them that is because of how much we sweat. They made me two very nice tweed suits, but already they have these weird white lines. I couldn’t work out what the lines were. Of course they’re salt. I have to peel off the clothes at the end of the night. I couldn’t get my tie off the other day because the entire thing was sopping wet. It’s keeping me fit!

The 39 Steps is becoming more and more global, it has opened in another five countries and they’re looking to do 15 more. We had a group of Korean people come in as they’re opening it in Korea now. The mind boggles. The thought of Korean Hannays running about is amazing. It would be really interesting to have a meeting of all the different 39 Steps cast from around the world, or maybe a website so we could swap tips and chat. I know in America they’ve made it slightly different. They tried bringing some of the jokes from there to here, but some of them work and some of them don’t.

- Jo Stone-Fewings was speaking to Kate Jackson


The 39 Steps is currently booking at the Criterion Theatre through to 7 February 2009. The current cast also features Josefina Gabrielle, Simon Gregor and Martyn Ellis. Maria Aitken directs.