How we met: Bonnie Langford & Sandi Toksvig

Sandi Toksvig, 49, began her comedy career in the Cambridge Footlights. She has since appeared regularly on TV, on such programmes as Have I Got News For You and Call My Bluff. She is also the author of 13 books, and was the first ever woman to chair The News Quiz on Radio 4. This year she was named broadcaster of the year by the Broadcast Press Guild. She has three children and lives in Surrey.

I met Bonnie 26 years ago when I was 23. She was handing over to me after presenting a season of live kids' TV. Most people at this point would be on their knees. All I remember is that she was as fantastically bright, energetic and bubbly off-screen as she was on. I have to say in all the time we've been friends, I cannot recall ever once seeing her depressed or in a fug. Without doubt she has got to be the most relentlessly cheerful person I know.

Our paths crossed again when her step-daughter turned up in the same class as my daughter. We used to meet every day at the school gates and have a right old laugh. The school asked us to do a fundraiser in the local church. For some reason it set us both off in the most impossible fit of giggles. Bonnie can be extremely irreverent. We ended up having to do the entire show without looking at each other. She has a great ability to hold it together as I stand there bent double, weeping with laughter.

We have very similar attitudes both on- and off-stage. Whenever I pop round to her house, despite her upbringing, there's never any sense of showbiz. It's an attitude that comes from a total disinterest in fame and celebrity. After our shows we don't drink champagne. Instead we go, just the two of us, and have a coffee. It's very low-key. Her attitude is - it's a job, a lovely job and when you finish you just go home. She's immensely down to earth.

I did a show on LBC which I invited Bonnie to co-present with me once a week. Ever since then it's been my ambition to show people the other side to her. She might well be able to get her ankle up behind her ear, which is a very good skill to have, but she's much cleverer than people realise. She interviewed many politicians and was always making comments that would make me go "gosh, that's clever, I wish I'd thought to say that."

Last year we went on a 35-date tour together - you have to be pretty close to someone to carry that off. She was the organised one. She'd hang all her dresses in the dressing room and lay out all her make-up while I'd sit there eating Marks and Spencer sandwiches reading the Spectator. Then she'd say, "Right we'd better do the show now," and I'd say, "OK". I've been known to go off at tangents right in the middle of the show and she always goes with it. I've never seen her hesitate or look at me as if to say "Are you mad?" She's an old pro.

Singer and dancer Bonnie Langford, 46, started her career on Opportunity Knocks aged six. Attending the Italia Conti school, she appeared in the musicals Cats and Chicago and the film Bugsy Malone. In 2006 she was a contestant on ITV's first Dancing on Ice. She lives in Surrey with her husband, daughter and step-daughter.

Sandi and I couldn't be more different. She did really well at school and went to university. I left school at 15 and was earning a living in Cats by the age of 16. What draws us together is the same sense of humour; we have extremely silly conversations which flip between politics, philosophy or world affairs to something stupid seconds later. There's no limit to conversation with her.

Sandi's brain is unbelievable. She eats up facts. She was brought up for a while in the States and used to get the train and go and watch the shows on Broadway. She has a huge love of theatre. I find it fascinating and we talk about it constantly. It's not what I would have ever predicted she was like. I'm also totally in awe of her writing - all those books she's written. I say to her, "how many have you done this week?" and she'll say, "Oh, just the one?'' It takes me that long to write an email.

Going on tour with Sandi is chaotic. We don't have a conventional way of doing things, in fact we have no idea how we're even going to get to any of the venues on our tour which starts this week. She's on her way round to mine now to hopefully sort it out.

When she did her radio show for LBC she invited me to join her because she knew she could chat to me endlessly. She said that whatever guest she had on, I would integrate and that I would know when she would need me to step in occasionally and when to keep my mouth shut. But generally we would just sit there and howl with laughter. Our producer would often have to shout in our ears or cut to a commercial break before it descended into total lunacy. That's what our show is in effect now - it's our friendship brought to the stage.

The other day we were in the dressing room and I'd just put a load of hairspray under my armpits thinking it was deodorant. I was walking around with my hands in the air and she was sitting there idly talking about make-up. I turned round and I said "hang on Sandi, what's going on? I'm the one whose meant to be talking about make-up and you're meant to be talking about Iraq and stuff. We've swapped places." People are intrigued by our friendship. I'm supposed to Mrs Showbiz and she's the Radio 4 voice of reason but in fact the combination is very different. You come across a lot of people in this business and there's very few you really want to stay friends with. Those are the ones that you really cherish. s

Sandi Toksvig and Bonnie Langford's 'Short and Curly' starts 22 May. Visit www.shortandcurly.info