Hi Lily and Eddie,
A good question. The play was premiered in 1983 though Berkoff wrote it earlier (I need to check when). I don't think the play is bound to a particular time period, I think it remains valid now. The time period will be the 70s and 80s (assuming he wrote it in the 70s), if you are looking at the context I would take this.
Does this help? Let us know about your project, it sounds interesting.
Iain
Iain