Blast Theory's experiment in crowd control

Theatre: Stampede; ICA,London

Blast Theory's last piece of work, Chemical Wedding, had its audience corralled in a roped-off area of the Queen Elizabeth Hall foyer, watched over by huge screens on which computerised images of viruses danced, mirrored on the floor by dancers pushing their way through the crowd to loud, industrial music.

The experience felt more like a scaled-down rave than a piece of theatre, though it was a thoughtful work about Aids and the metaphors of infection, and it attracted an enviably mixed audience.

During the performance the company got some first-hand knowledge of the techniques of crowd control, which they decided to exploit for the new piece, Stampede. "Looking at crowds is a way of pulling form and content together," says Matt Adams. "We started working on it shortly after the poll-tax riot, which was the peak experience of my life - being simultaneously empowered and scared, it was emotionally devastating."

Stampede obliquely explores the Criminal Justice Bill and Operation Spanner. "We felt a real desire to look at the point of declaring yourself publicly. At what point do you make public your beliefs, and in what ways?" Adams asks.

The audience is encouraged to intervene during the action by operating pressure pads which in turn activate video and tape samples of the "10 stages of rioting" from police training sources, and mind control techniques identified by the Cult Information Centre. For the technical side of the show, Blast Theory has inveigled the help of the first students on the Royal College of Art's interactive multimedia MA, and the technological aspect of the work clearly attracts a different kind of audience than the usual ICA avant-gardists. But still, the impetus is political.

"The promenade format allows people a sense of themselves as a group, they can move around, stop watching if they get bored. You can also convey more excitement if what's happening is right beside you rather than 25ft away," Adams says. "We don't have a political message as such, but our hope is that in the end you think about an individual taking an action." The only problem is the passivity of the audiences. "They tend to be more timid and nervous than the performers, and when people are too self- conscious, it can prevent them really engaging with the piece."

n `Stampede' is at the ICA, London (0171-930 3647), from Thursday. Clare Bayley chairs a post-show discussion on Friday