It’s months since I saw Teh Internet Is Serious Business at the Royal Court in London, but the evening has remained memorable, not so much for the play or its boisterous production, but for some members of the audience. I was sitting in the cheap rows at the front of the stalls; ahead of me was a group of women, in their late teens or very early 20s. They chatted quietly as they waited for the lights to go down, and then, as the actors began speaking, three of the women pulled out McDonald’s bags and started to eat. At first I was astonished by their chutzpah, then by the fact that none of the staff came to scold them. The performers were close enough to lean over and grab a chip if they wanted to. Were they disturbed? They didn’t seem to be.

Pretty soon, the women became part of the landscape of the play: at one with the characters’ crackling disregard for social norms. But they weren’t disruptive at all. (And no, the food didn’t smell.) I kept glancing at them throughout the show; in the first half, they seemed politely interested, but by the second, their attention was rapt. The theatre-makers couldn’t have asked for a more engaged and appreciative response.

I talked about those women at a recent event at Battersea Arts Centre in London, hosted by Jess Thom and theatre-maker Jess Mabel Jones. Thom has Tourette’s syndrome and her tics make it impossible for her to be silent and still when watching a performance; as a result, she has been made to feel unwelcome by other audience members, and for many years stopped going to the theatre altogether. The gradual introduction of one-off “relaxed” performances, aimed at people with disabilities and their carers, have given her greater access, but these are still few and far between.

A vital question was raised at the event: what might the theatre landscape look like if it were more relaxed, not occasionally, but all the time? Last summer, a Theatre Charter was proposed, detailing expected behaviour for the benefit of occasional theatregoers: no rustling sweet wrappers, no mobile phones, definitely no eating McDonald’s. How much more inviting might theatres feel if they didn’t just reject the snobbery embedded in such a charter, but offered a different manifesto, in which it was clear that all people – whatever their backgrounds, ages, physical or mental abilities – were welcome to see any performance, any day they wanted, together?

Jess Thom, who has Tourette’s: eradicate stigma. Photograph: Richard Saker/The Guardian

For an art form so dedicated to thinking about human behaviour and interactions, theatre is remarkably bad at allowing its audiences to be human beings once they take their seats. You might have bought your ticket weeks before, but if you’ve had the bad luck to catch a cold in the interim and enter the auditorium with a cough, you can expect to be pretty much despised. And disability is much more stigmatised. As Thom points out, a fifth of the population identifies itself as disabled – and that, she argues, is a lot of people to block or discourage from coming to the theatre.

None of this is what theatre should be – and at the root of the problem is the expectation that people in an auditorium should be homogeneous, conforming and undifferentiated, so as not to distract either the performers or each other. But the whole point of theatre is that disruption should be possible: that’s what it means to be live. In rejecting the Theatre Charter, Amber Massie-Blomfield, head of communications at the Albany theatre in south London, invoked the “cat test”: devised by theatre-maker Chris Goode, this proposes that if a cat can wander across the stage and its presence be acknowledged and accommodated, the action is genuinely live. Anything else might as well be cinema.

Thom, Jones and a cohort of theatre-makers are working on a variety of proposals to extend “relaxed” performances beyond the limited, one-off events that they are now. One includes changing the name to “extra-live” performances, to eradicate stigma and communicate the fact that seeing the show with a more diverse audience is actually truer to the spirit of theatre. Another involves declaring most performances “relaxed” and creating the occasional “uptight” performance, for those people who like to watch their theatre in a more elite atmosphere. Another invites theatres to advertise themselves as “relaxed” buildings, where all are welcome and all behaviours can be accommodated. Thom has written a thoughtful blog post assessing the merits and drawbacks of these approaches.

As a regular theatregoer, I admit that in the past I would have assumed that “relaxed” performances weren’t for me. Happening by chance to see a couple of plays with Thom in the audience changed my mind. Far from proving a distraction, her tics not only illuminated aspects of each show, but became less visible and audible the more absorbed I became by what I was watching. Thom has this experience often: at BAC she told a story of a man who discovered on arriving at a theatre that he had accidentally booked for a “relaxed” performance, and tweeted his disappointment and regret. At the end, he tweeted again, to say he had had a brilliant time – a significantly better time, he thought, than if he had attended a non-relaxed show. If more people attended “relaxed” performances, Thom argues, more would see that their assumptions about people with disabilities are false. As well as benefiting theatre by extending its audience, breaking down those assumptions might just benefit society.