Writing recently for Exeunt, Catherine Love recalled an experience that epitomises the Edinburgh Fringe for her. It was hearing a play read in the Traverse bar, producing “some strange theatrical alchemy…a perfect demonstration of how sometimes, with just an actor, a script and a few gathered audience members, theatre can charge the atmosphere of a room”. That play was Clara Brennan’s Spine. This year it’s back, this time at the Underbelly, and has been transformed from a 15-minute short into a full hour’s monologue.

Spine was originally written for Theatre Uncut, which is now in its fourth year responding to the government spending review. “Each year it gets harder,” says Brennan. “Do I want to write a play about the NHS, or the closure of rape crisis centres, or education? The closure of Kensal Rise Library really captured my imagination, so I’ve been following that story really closely.” The library was opened in 1900 by Mark Twain, but has been closed (along with four other libraries) by the (Labour) Brent Council. “They came stealthily in the night; they stripped the murals and took all the books out at 2am,” explains Brennan. “In Spine an elderly lady, Glenda, has stolen the entire contents of that library to keep safe as a sort of legacy to give back to the community. I started there, but I wanted to write about a disenfranchised younger character, a teenaged called Amy, so the story comes from her. So it’s still a one woman show, but she impersonates Glenda – badly at times – and all the other characters as well.”

Brennan has been able to use the experiences of watching those early versions of the monologue to develop it into the longer form in which it now stands. Rosie Wyatt, who did the initial reading at the Traverse, is back playing Amy. “It’s good fun to write with that in mind, and to be ambitious in that respect. I’ve just been doing the final finessing of the draft, and knowing that Rosie is on board, I can hear her voice and think, what can I push this actress to do? I was really aware that if you ask a young actress to come to Edinburgh and do a show then you want to give them a meaty part. I’m always really inspired to write for women. There’s a dearth of decent female parts – I’m not trying to redress the cannon, but you know.”

The monologue form – direct, focused storytelling – suits the political tenor of Brennan’s play. “A monologue should be the moment at which a character must speak. For me there’s a really exciting dramatic possibility about someone going… [at this point Brennan opens her mouth and makes a splurging sound].” The monologue’s the moment at which something necessary bursts out of a character, an instinctive compulsion. “You realise that even if you’ve written something miniature, you’ve got a strange sense of the backstories, latent underneath.”

Brennan is particularly aware of the need to synthesise the political focus with the human force of the storytelling. “What we’re working with is empathy. An actor literally puts themselves in another person’s shoes. The human element is trying to make it funny and engaging. In the first draft of Spine I was aware I was using Amy the character as a mouthpiece and I felt the whole audience resist and sit back, and I thought, fuck I’ve lost them, so I rewrote it to just dramatise her politics in an Amy way.

“That in itself is a manipulation, I’m really aware of that. Previously at the end of the play Amy said ‘this is my manifesto’, and there was a real sense that Glenda had given her the mantle, and she was actually keen to create her own Party – that felt way off the mark in terms of where that character was. Amy is still really reluctant to be a political leader in that way.”

Although on the face of it Spine is a monologue, it’s one that seeks to open up and dramatise productive political dialogue, both between its characters and with its audiences. “I’m really enjoying the intergenerational conversation – that dialogue is key to the piece. Glenda describes her husband coming back from the war and the building of the NHS and the state, and asks questions like, what were we fighting for – this was the golden age. They talk a lot about the imagination, a different world: don’t just receive the ideas of the main political parties. Think about what you actually require, and if they’re not ticking those boxes then do it yourself.

“There’s a real sense of trying to galvanise young people, and this comes from my only thesis – young people should be angrier than they are. Theatre Uncut was born out of fury and frustration – I think theatre’s good for venting that, and beginning dialogues. I hope one of the selling points is that this is a play which is pan-generational. The audiences of Theatre Uncut are young and old. It’s not until you speak to your audience after a show, let them speak, that you realise this demographic is not necessarily the straightforwardly liberal one you thought it was, and this is really exciting to me.”

This again feeds back into the form and staging of the play, harnessing the strengths of the Edinburgh setup. “Studio spaces work really well. There’s definitely something in direct address which implicates us, and listening in depth to an hour’s story from a character is quite a privilege. There’s something about direct address which is in its own way politically potent, speaking out, addressing the audience members so that they never forget that they’re there.”

Brennan indicates that Edinburgh, with its audiences trained on comedy and small-studio theatre, offers a uniquely concentrated and suitable environment for this type of theatre. “A while back ‘big P’ Political theatre wasn’t very fashionable. I think it’s exciting to combine working class storytelling and comedy with a political edge. I wish that theatre was as exciting to the nation as football is.”

And in Edinburgh, during August, there’s the momentary illusion that it just about might be.

Spine is playing at 15:30 at the Underbelly throughout the Edinburgh Fringe. For more information and tickets, visit the EdFringe website.