This year is Cardboard Citizens' 25th anniversary and we decided to mark it by putting together a book to tell our story to date. The act of recall has been a labour of love and wonder, tinged with sadness: love, to think of all the amazing friends who have been part of our journey; wonder, in thinking, wow, did we really do all those things (when we had no idea of how to do anything); sadness, that some of the Cardboard Citizens didn't make it through to 2017.

When you start out, you have no idea how important it might be 25 years down the line to keep the irritating pile of documents that quickly accumulates. We certainly had no idea that what started as an exploratory project to prove a theory would ever end up as an enduring living breathing organisation with a life of its own, whose effects have been felt both by thousands of individuals we have met on our way and by companies and organisations worldwide who have been inspired by Cardboard Citizens to create their own projects with homeless people.

The group was one of the most generous, tolerant and non-judgemental I had ever facilitated

I first bought a book by Augusto Boal in 1976. I found The Theatre of the Oppressed exciting but difficult to read, and skipped to the end to scan the few practical exercises offered almost as a postscript. In the late 1980s I encountered the work again, in workshops with Boal himself, and ended up inviting him to London to deliver a workshop at London Bubble, where I was working as associate director.

My prescient boss at the time, artistic director Jonathan Petherbridge, suggested that we apply for funds to put these principles into action, trialling Forum Theatre in London. We created a list of the type of ‘oppressed' groups we might be interested in working with; the list was long, including unemployed people, nurses, teachers, people with mental health issues, disabled people, prisoners, youth workers, women, you name it.

This was the tail end of a turbulent period of British history. The Big Bang had happened in the city, brash yuppies brayed openly of their wealth, and politicians spoke of (the inconvenience of) stepping over homeless people in doorways on their way to the opera. Suffice it to say, political opinions were polarised. Eventually, by a process of elimination, we arrived at the idea of working with homeless people.

We stuck up posters in day centres around London, advertising workshops in those venues – 'Homeless? Got something to say about it? Come to xyz'. The idea of theatre helping people barely existed at this point, so while most organisations and centres were happy enough to work with us, from the start we had to try to explain what we were doing and why – which was a tough call in some respects, as we barely knew ourselves – we were making it up as we went along.

We had the pleasure of performing under a railway arch to some 70 well-lubricated and jovial members

On the back of these first outreach workshops, we invited any homeless people who wanted to come to what was effectively planned as an audition workshop. A wonderfully varied group of some 18 people turned up to take part – street-sleepers, sofa surfers, drug users, trans women, students, sex workers (male and female), people with learning difficulties, migrants, old, young, gay, straight – the group was virtually a snapshot of social exclusion at the time and a premonition of the many constituencies that would come to make up the company in future years. The workshop itself was amazing – this heterogeneous group was one of the most generous, tolerant and non-judgemental I had ever facilitated, and their stories came tumbling out.

Over the next two weeks, we shared stories and improvised scenes till we had cobbled together two plays based on the lives of our group. We put together a short tour of London hostels and day centres, and off we went, learning rapidly on the job, playing purely to homeless audiences and those who worked with them.

At that time, there were two settlements of street-dwelling homeless people in London, going by the generic name of Cardboard City. The largest of these was the Bullring, at a vast paved underpass in Waterloo, now occupied by the IMAX cinema. This alternative metropolis of lost souls and renegades encompassed some 200 people living in improvised cardboard ‘bashes', some of which had been there long enough to receive regular postal deliveries.

The idea of theatre helping people barely existed at the point we were beginning

The culmination of that first-three week tour took us, by invitation, to the Bullring, where we had the pleasure of performing under a railway arch to some 70 well-lubricated and jovial members of that community (as well as 15 or so dogs plus the local vicar), on a wild night which took our rather strait-laced reading of Forum Theatre to whole new areas of chaotic beauty and possibility.

The group started meeting regularly and Gary Gallard, an important founder member, came up with the name Cardboard Citizens. More plays were made, more tours executed, plans for independence were hatched, and four years down the line the company became an independent entity.

Year on year we have gone forward, operated part-time, then full-time, grown, shrunk, grown again – lost people, found people, added functions, tried things, come close to extinction, clawed our way back, got stronger; moving several times, from an office under a hostel until we arrived at the glorious premises we currently lease in Whitechapel, complete with our own workshop space. And here we are, celebrating 25 years, with the world premiere of nine plays charting 150 years of the history of housing the poor, at The Bunker, just a 15 minute walk from where it started in Waterloo. We hope you'll join us there to celebrate this milestone.

Home Truths runs at the Bunker Theatre until 13 May. Cardboard Citizens 25 Years is available to buy now. Please email [email protected] if you would like to purchase a copy.