Phoebe Waller-Bridge in Fleabag at the Big Belly, Underbelly.

“People immediately assume it’s you”, says Phoebe Waller-Bridge when I ask about the challenges of performing her own writing. “We had that conversation early on – it’s just a badge I’ll have to wear.” It’s one that many would shrink away from; Fleabag, developed with the other half of Drywrite, director Vicky Jones, includes snort-out-loud graphic accounts of drunken hookups, all-night wank sessions and an unspeakable act performed on a hamster. One of the most talked about shows of this year’s Edinburgh Fringe, Drywrite’s touchingly funny one-woman piece about a self-obsessed, sex-obsessed twenty-something has garnered multiple awards and recently transferred to London’s Soho Theatre.

Played by Waller-Bridge, the titular Fleabag began as “someone that was quite close to us and the women we know”, Jones explains, “but increasingly became someone further away from us – a slightly younger generation and a product of her environment, of the media and porn industry influence that she’d grown up with”. It’s certainly difficult to match up the two clean-cut, professional sounding women sitting across the table with the frank filth spewed onstage, as we chat politely over cappuccinos in a private members’ club in Soho. Every now and then though, one will crack and set the other off into raucous laughter as the duo, whose partnership veers between “abusive marriage” and creative “love affair”, talk sex, sexism and success.

Born out of a ten-minute standup routine (then “a lot of late nights in the kitchen” and “so many bottles of wine”) the Fleabag character wasn’t intended to be obsessed with sex. After the original short “went down well on the night”, Waller-Bridge tried “to explore other journeys for her, but it kept coming back that instinctively the play was about this over-sexualised culture. It’s a theme we’ve wanted to talk about for ages. Once we realised that I was accidentally starting to knock on the door of that conversation, we started getting excited about how much we could pull it out.”

The character isn’t a victim of sexual abuse, though they imply this may have been an ending at one point: an early version, about which they are “sworn to secrecy by our producer… went too far – it was hugely extreme and defined the play as something else”. Instead, the unnamed woman is a casualty of culture: the logical conclusion of a society saturated by what Jones calls “the onslaught of images” of commodified sex.

“It feels like a bit of a trick really,” says Waller-Bridge on hitting at these ideas with comedy. “We realised that once you’ve got the audience laughing, it seems like a waste not to pull them right back.” The jokes in Fleabag aren’t a balancer for the dark stuff, but for the medium itself: through the comedy, Waller-Bridge explains, “you realise how much pain [the character] is deflecting; no one attempts to be this funny all the time so that’s obviously where the loneliness is – it’s about teasing that out without pressing it too hard.”

The compelling conflict of Fleabag, as its performer says, is that it “doesn’t have all the answers”; a key inspiration was “a feminist lecture where [in the play] the girls are asked whether they’d take five years off their lives for the perfect body”. When Jones and Waller-Bridge had discussed this, “we’d secretly whispered that yes, we would. The implication,” Jones says, “was that this was the anti-feminist thing to say; how can you be a feminist and hate your body? But the two things aren’t mutually exclusive – we’re products of our environment. We’re all part of this culture and we all buy into the objectification of women’s bodies, so we wanted to write a character who’s a product of the world that we see now, as opposed to a leading light of feminism.”

The show’s August run, which won Drywrite a Fringe First and Waller-Bridge a Best Solo Performance award from The Stage, was part of a “brilliant Edinburgh for women and feminism”; the two talk enthusiastically about Bryony Kimmings’s Credible Likeable Superstar Role Model (“really moving”, “gorgeous”) and Bridget Christie’s Comedy Award for A Bic for Her. “It feels like feminism is being talked about in so many different ways now,” says Waller-Bridge. “Women are tapping into it as an idea for theatre and comedy in such exciting ways. Eventually though, you want it to be normal and not novel. People are going crazy because two girls have written a play about a girl and boys are finding it funny. It’s like, ‘stop the press, something’s going on here!'”

Is Fleabag a feminist action? “Absolutely”, Waller-Bridge nods. “As an actress there are so few ugly characters – both aesthetically and in terms of personality – onstage and onscreen, so it was this hunger for that that drove Fleabag, knowing that I’d get to play her. It feels like such a step forward to play someone that isn’t perfect, or trying to seduce the audience or anyone else – it’s really liberating.” Jones adds: “There aren’t enough of those sorts of roles for women. The only thing we can do is keep trying to write them.”

With the Soho run and a potential TV adaptation ahead, Jones and Waller-Bridge won’t be putting Fleabag to bed anytime soon. Is she a fun character to play? The actor’s eyes light up “Yeah.” Does she feel like she’s going mad, inhabiting the neurotic nympho every night? “I actually feel really free – I feel mad the rest of the time! There’s something so electrifying about that moment where you don’t know how people are going to respond – that’s part of the thrill.” Whilst Fleabag’s success so far has been an exciting surprise – “Phoebe hadn’t even planned who she was going to thank” for the Stage award – Drywrite isn’t going to let a couple of commendations get in the way of more hard graft: “the moment you get anyone saying ‘well done’,” Waller-Bridge says seriously, “is the moment to run back and work harder. I think that’s probably what we’ll do…” She laughs and looks at Jones – “I mean, it is what we’re doing.”

Fleabag is at Soho Theatre until 22 September.