A group of young, predominantly black young people are sitting in a semi-circle debating the strengths and weaknesses of a film script about a fictional girl gang, set amid the seedy tower blocks of East London's under-class.

The film is called Sket – street-speak for prostitute – and its writer, Nirpal Bhogal, listens intently as a woman wearing a pink fedora challenges him on a certain phrase in his first draft – which incorporates themes of gang rape, violent revenge and brutal initiation ceremonies – that does not ring true. Anyone listening to the discussion might mistake the woman for a member of the film crew, picking up a stylistic script error at a pre-production team meeting. But "Antique" is a resident of South London and she has come to the Eternal Life Support Centre (ELSC) in Peckham to reveal the brutal inner workings of the capital's growing number of girl gangs. The insights that she conveys to Mr Bhogal come from experiences and eye witness accounts of gang culture that the film hopes to bring to life for cinema audiences next year. Today's meeting is one of a series of consultations that the film's producer, Nick Taussig, has set up with South London youths who have been closely linked to girl gangs.

Advisers at the Damilola Taylor Trust referred film-makers to this office in Peckham, a stone's throw from the library which Taylor visited shortly before he was murdered 10 years ago, so they could enlist these youths for their workshops. While some will advise filmmakers on its script and music, others will be selected to star in the drama. Sket's storyline revolves around a 15-year-old girl living in an East London estate, who seeks revenge after her brother is beaten up and blinded.

The girl, Kayla, joins a local girl gang for this purpose, undergoing a series of initiation exercises which include theft and violence to convince the gang leader, Danielle, of her genuine intent, but then finds it difficult to break free. The film, being made by Gunslinger, the production arm of Revolver Entertainment, which distributed Noel Clarke's gritty urban drama, Kidulthood, is searching for a new kind of cinematic authenticity producers hope will balance the clichés and cultural stereotypes often seen in gang films.

"There is a distinct lack of public knowledge about female gang culture, which results in a high level of fascination," said Mr Taussig. "The unique idea behind this film is wholly based on reality. All events have been taken from first-person accounts, accuracy is key. This is especially important in making sure the film resonates with audiences."

The workshops in Peckham have provided invaluable material: two girls from a previous consultation of this kind, who are still active in gangs, helped to shape two of the film's central characters including Danielle. Even Jennifer Blake, the managing director of ELSC – a charity which supports young people – can talk about gang culture from personal experience. Ms Blake, now 42, joined a gang at the age of 13, when she became known as "Shine-Eye" and she rose to become its leader, initially making a living from a protection racket and moving on to bigger, violent crimes in her 20s.

"I left home at 13 and ended up in care... I had a lot of influence over people as a leader and it can feel powerful. At the age of 18, I began doing bigger things but as well as the lifestyle it gave me, I ended up being kidnapped, tortured, beaten up. It's a choice you make to join a gang but it's not a simple choice to walk away... I have two children and they got caught up in my lifestyle. It's not a good example for children," she said.

Blake felt the workshop was valuable for combating myths about life inside girl gangs. "The way they are portrayed in the media is not very real; they are shown as a loud group of girls but the girls are also victims. Gangs are the "in" thing and if you are not part of something, you're nothing. "You might see them making noises on the street but behind closed doors they are sometimes suicidal; I almost ended up in a mental institution.

"But when you're with your peers you show that you can handle it, that you're ok," she said. Bhogal said he was keen to set up the workshops for the same reason, and also because he wanted to replicate the language of the street. Some of the language in his first draft did not chime with the 12 youths in the room – terms for having sex range from "having a ting" to "beating someone up".

The discussion is open and what is worn, drunk and smoked is fully elucidated by the group; girls in gangs tend to drink spirits and wine more than their male counterparts, who more commonly smoke cannabis.

While male gangs are more likely to carry guns, girl gang members will use knives, shoe heels, combs, bricks, bottles and even keys in attacks. Initiation into a gang is vital, and this is most often done through violent attack: "You have to bung up someone to prove you are tough. Normally they (the victims) have got to be innocent just to prove your point."

Dwayne, a 26-year-old local resident said while he was gripped by the script's storyline, he felt one particular scene when the girls attack a boy at a party was unconvincing due to its lack of strategic planning. "They would have sat down to discuss it and been prepared when they went inside."

Another older volunteer in the workshop said the most sophisticated gangs would not indulge in "happy-slapping" – or putting filmed violence on YouTube – because there would be no "business" advantage in doing this. As one teenager said: "Gangs are run like a business, but instead of getting fired, you get seriously hurt." The rule on cross-gender violence varies; some men veto any violence against girl gang members but to be a "top dog" or gang leader, violence against both sexes is deemed necessary. Cimone Walkers, 23, a graduate and resident of Lewisham who has never been a gang member but has observed gangs, said the power for women in girl gangs, ironically, sometimes came from a position of assumed submission to a man. "Women who allow themselves to be submissive, with a goal in sight, such as revenge, are a lot tougher. That girl has got a degree of protection to get her revenge. She is obviously more manipulative."

The Peckham Glossary

*Sket: Prostitute

*To rush: To attack as a gang

*To have a 'ting' / to beat: Have sex

*To chop someone: To kill them

*To bung up/to box: To beat up

*I feel him: I like him

*To wet someone: To stab

*Brethren: Fellow gang members

*Da fiend: Drug addict