Paul Wakelin, leader of the group, stands up and shouts: "My name is Paul: Power for Paul."
All eyes turn to Fatima Mirza, a 21-year-old third-year medical student from St Mary's Hospital, Paddington. With nine GCSEs and three A-levels, Fatima is struck dumb. It is clear that her mind has gone blank.
Ian Willis, a 35-year-old man with Down's syndrome, steps forward. He cannot read, has difficulty with words, and lives with his mother in Willesden Green. "How about frog?" he says. "Frog for Fatima." Relief sweeps over Fatima's face.
And that exemplifies the whole workshop. The eight learning-disabled actors are the leaders, the pace-setters, the people with experience, who know the ropes. The medical students do what they are told.
Dr Jack Piachaud, consultant in psychiatry at St Mary's, whose students are the prey, explains the significance of the afternoon. "It is about positive imagery. All the roles are reversed. The people with the learning disabilities take charge," he says. "It introduces students to people with learning disabilities in a non-clinical setting. They see them as people first. It is a leveller: together, they are finding the commonalities. The clinical approach is always looking at the differences."
Students from St Mary's have been attending the workshops for six years, although the company has been acting together for much longer. It was set up in 1982 from a drama group, formed at the Strathcona social education centre in Wembley. Its play, Pain without, power within, opens in London next week before starting a four-week tour of Britain.
For five minutes, the actors instruct the students in stretching, miming, and getting-to-know-you games. Then the two company directors ask everyone to divide into small groups and construct, out of their bodies, a word, a piece of equipment (a hosepipe, a harp, an electric chair are some of the results) and, finally, a silent tableau.
After two hours, all traces of self-consciousness have disappeared, as have barriers between the two groups. They have worked together, laughed together and made fools of themselves together.
The actors are satisfied. "I love acting. I want to be a movie star," says Sheldon Antoine, a handsome and athletic 22-year-old from Swiss Cottage. "That is what I am hoping for. I would like to play with Arnold Schwarzenegger.
"I have difficulties reading and writing, but at least I am doing something, not sitting at home on my arse all day long," he adds.
Julie Mathurin, 21, who lives with her family in Ladbroke Grove, is hoping to become a permanent member of the troupe. She says her problem is that she is a bit slow.
"At college they said they wanted me at first, but then they said I was too slow. I am slow at reading and writing and things like washing up.
"My sister, who is 15, is prejudiced. She says I am spastic and stupid and laughs at me with her friends. One day I will show her. One day she will look back and feel sorry for what she did."
But does the workshop achieve what it sets out to do? A study by Professor Sheila Hollins, of the division of the psychiatry of disability at St George's Hospital Medical School, London, whose students also participate in workshops, suggests that it does.
One group of students was given questionnaires both before and after a workshop, with such statements as: "people with Down's syndrome are poor communicators" or "people with Down's syndrome act like children most of the time".
There was a marked switch in attitude. The percentage of those who agreed with the first statement fell from 36 per cent before the workshop to 16 per cent afterwards, while those who agreed with the second statement, fell from 39 per cent to 13 per cent.
"We feel we have demonstrated the value of the workshop in changing attitudes to a more enlightened viewpoint," Professor Hollins says.
The company, which can pay its eight actors only pounds 65 a month because, otherwise, their disability benefits are affected, is also convinced that the work is necessary. One of its two directors, Ian McCurrach, says that working with medical students is particularly valuable. "The first point of contact for someone with a potentially handicapped child is a doctor, so it is important that they have a positive image of disabled people."
So has the exercise altered the perceptions of the St Mary's students? Most seem to think it has.
James Kennedy, a third-year student from Hertfordshire, says: "Despite the fact that I have got a handicapped cousin, I find it difficult to talk to handicapped people. I am worried about seeming condescending.
"But coming this afternoon, there was no barrier. Any barrier that I had envisaged was artificial, because they took the lead and showed us what to do."
Libby Swallow, another third year, says: "The games were such fun to do that we were all communicating very well. When you got into the games, you forgot that they were disabled."
The only sad aspect of a positive afternoon was the fact that out of 25 students who were meant to participate, only 13 turned up. Of those who did, not all used the politically correct "learning-disabled" for the participants, preferring the old term "mentally handicapped".
'Pain without, power within' is at the Cochrane Theatre, London, on 30 May and 1 June. For details of the June tour call Strathcona Theatre Company: 0171-403 9316.Reuse content