Posing Martin Creed beside his dancers, the photographer suggests that he might put his arms out, as if directing their steps? "But I don't do that," explains Creed, holding his arms resolutely by his sides. Then he crosses them: "Actually, I'm usually in a straitjacket... "
It's true that Creed has very undancey body language. The Turner Prize-winning artist is working with dancers for the first time: a choreographer with no dance background. His new project, Work No. 1020, is presented by Frieze Music and Sadler's Wells, as part of a season marking the centenary of Diaghilev's Ballets Russes. Diaghilev's groundbreaking company encouraged collaboration between the arts. The Sadler's Wells season celebrates it with new works rather than revivals, including Creed's first steps in ballet.
Diaghilev commissioned Picasso and Matisse for his ballet company, a fact that Creed obviously enjoys. "I always thought that looked brilliant," he says. "When I first started learning about art, I thought that was part of what artists did, getting involved in ballet and stuff like that."
Work No. 1020 is part of a dance/art crossover season, but it follows Creed's own interests. Last year, his Work No. 850 set runners sprinting through the Duveen Galleries of Tate Britain, negotiating the crowds of visitors. Asked why he's taken to dance, Creed goes back to his runners. "The idea of that was to do a piece where a person moves as quickly as they can. After that, I thought of trying to slow down the movement. Classical ballet, and different forms of dance, provide the movement of the human body broken into different kinds."
Creed is an appealing but very careful speaker. Explaining his work, he'll go back over the same point, refining what he's saying, with pauses, "ahs" and soft Scottish "ems". They're not the "ahs" of someone who isn't sure what to say. Creed wants to get it right. He's ready to wait for precisely the right word, watching other people to be sure they understand him.
Aged 40, Creed grew up in Glasgow and studied at the Slade School of Art. He numbers his works, often with descriptive subtitles: "A large piece of furniture partially obscuring a door", or "The lights going on and off". This last work, which won the Turner Prize in 2001, did exactly that: a pair of lights flashed on and off in an empty gallery. "In my work, in the years gone by, I've tried to make work that doesn't use extra materials," Creed says now. "Like the lights going on and off, which just uses the gallery, as it is. So to me, trying to use the human body is one step further in trying to make work that doesn't add things to the world. It's not adding extra stuff, it's people."
With Work No. 1020, Creed isn't adding extra stuff to dance, either. He starts and ends with the five basic positions of classical ballet. Those are his only steps. The dancers can move forwards, backwards or sideways: no diagonals. As in many rehearsal rooms, the floor of the dance studio is marked with tape lines – but Creed has an awful lot of them. His dancers literally step from mark to mark: the length of every step has been measured.
"I had the idea, without knowing anything about classical ballet, to try to make a dance where every position is equal," says Creed. "Then I tried to find out about ballet, and how that might work, so that's when I found out about the five positions."
Working with five dancers and rehearsal director, Lorena Randi, Creed is building those basic positions into dance sequences. His choreography is highly patterned, with strict rules governing the order and duration of each pose. Over the course of this rehearsal, I can see Randi helping to turn Creed's ideas into dance, dealing with the practicalities of dancers' bodies. Stepping sideways, they tend to move slightly forwards: their ballet-trained feet turn out to the side, but not quite to 90 degrees. They need to compensate, sloping lines becoming straight.
It's the same with the positions themselves. In one sequence, Creed wants a contrast of horizontal and vertical. "But then I find that in the correct classical ballet position, the arms are higher than horizontal. So we discuss things like that – she has helped me translate that into equivalent ballet movements."
It's a cheerful, giggly process. Creed watches, stepping up to check angles, retreating again as the line of women moves onwards. One sequence involves dancers moving at different speeds. When it comes to held poses, that's tricky for the woman left standing on one leg for five counts. Laughter breaks out as she wobbles. They all stop, stretch their muscles, start again. Randi and Creed stop to discuss how long the balance needs to last, how tough it's going to be.
There's no hierarchy within the cast. "They're all equal. They're examples of different people. Sometimes when they're all doing the same thing, that's a good way of showing you the differences, between their bodies and their personalities."
His dancers are all women, apparently because it's easier: there are just more girls learning ballet than boys. "I did think there should be equal women and men. That might be the next thing, because I think of it as looking at examples of different people living their lives. And that's incomplete without there being men there as well."
In another recent work, Creed wrote orchestral music where each note was played at the same time, by instruments arranged in order of pitch. "The idea is that all notes are equal, all instruments are equal." His new dance tries similar ideas. "I'm trying to make a dance where they hold positions for about the same time as the movement, with movement and stillness being balanced." In some sequences, the step pattern also drives the music. "In some of the bits you've seen, each position has a note. So C, D, E, F, G is 1, 2, 3, 4, 5. You could say that the dancers are leading the music, because whatever position they're in determines the note."
Some of Creed's dances aren't that different from more conventional ballets: it's not uncommon to watch dancers walking forward, stepping from pose to academic pose. It's much more surprising to see that sequence run backwards, with dancers reversing through the same sequences, like a film played backwards.
Some of this choreography, Creed says, comes from "the way I don't feel sure what I want. A lot of the time, the dancers have to do the thing, then do it backwards. I find that beautiful, to do something and take it back. But that has its own technical difficulties." The steps have to come in a particular order, because that's the only way that works in reverse.
The dance-driven piano notes won't be the only music. Creed's own band will play live for the event; he plays the guitar, and sings. "The dance bits will probably be interspersed with songs," he says. "The amount of each is not yet decided – I'm trying to remain open about it. I want it to be easy and enjoyable. If there's too much of one thing, I want to be able to break from that."
He's very conscious that theatre events have "a trapped audience", unlike art galleries, where people are free to come and go. "That's the big difference. I like it when people are free. I like to be free myself. It's different if you're stuck in your seat." He's creating the dance in short sequences, so that he can move easily from music to dance, adjusting the evening's outline.
"I'm really aware that I haven't done a performance yet," Creed admits. "The only way to find out is by doing it live." He smiles suddenly. "I'm really scared about all of this," he says, sounding delighted. "I'm really excited and really scared. I've been working with these dances, different variations. I need to find out about it from performing it."
Is he likely to do more dance? "I'd like to. I find it endlessly enjoyable. And funny." Thinking about dance itself, he links it back to his earlier work. "Trying to make work with people rather than with brass or concrete, is to do with feeling myself. One of the facts is that I am constantly moving. Because I'm alive, my heart's beating. Movement is a sign of life. In a way, the minimum necessity of life is to move. Thinking, feeling, all those other things are added on top of that.
"If life is to do with moving, then living better – which is what I want to do, to live in a better way – maybe a way of trying to live better is to try to move better. Working with dancers is trying to work out ways of moving that are honed down, then presented for people to enjoy. In other words, watching a dance is like watching life, in a distilled way."
'Work No. 1020' runs as part of the Frieze Art Fair at the Lilian Baylis Studio, Sadler's Wells, London EC1 (0844 412 4300 or sadlerswells.com) 16 to 18 October