The screenwriter Jane Goldman freely admits that her new film Kick-Ass "is not, obviously, for everyone". Perhaps she is thinking of the scene in which Hit-Girl, an 11-year-old female assassin in a luminescent purple wig, enters a roomful of evil baddies and utters the immortal line: "OK you c**ts, let's see what you can do now." Or maybe she is referring to the bit where Hit-Girl, in a conversation with her father about what she wants for her birthday, pretends to ask for a puppy before admitting with a coquettish giggle that "I'm just fucking with you Daddy. I'll have a Benchmade model 42 butterfly knife." Or she could be recalling the moments where Hit-Girl shoots a man through his cheek or slices off a drug dealer's leg with a machete.
Whatever the reason, Goldman is aware that Kick-Ass could cause something of a stir. "I wouldn't take it personally if someone didn't enjoy the film," she says when we meet. "Certainly my 86-year-old friend of the family, I'd strongly recommend she doesn't go and see it."
She laughs, a tad uneasily. Goldman, 39, a talented writer who penned the widely-acclaimed 2007 film fantasy Stardust, is clearly nervous about how Kick-Ass will be received. "You've no idea how the audience is going to react, you just hold your breath," she says, anxiously pressing her hands together, her face partially obscured by a curtain of dyed carmine red hair. Later she will admit that she hates interviews. Partly, one imagines, this is because she happens to be married to the television presenter Jonathan Ross, he of the floppy hair and the inflated salary and the lewd answerphone messages, and she is wary of saying anything that could add to the public circus that surrounds him.
But in this case the nerves are misplaced. Kick-Ass is a brilliant and inventive piece of film-making and looks set to become one of the box-office hits of the year. It tells the story of Dave Lizewski, a nerdy high school student and comic book fan who decides to become a superhero despite the fact that he has no special powers. Dave (played by Aaron Johnson, who recently starred as the young John Lennon in Nowhere Boy) proves to be a fairly unsuccessful vigilante until fate brings him into contact with Hit-Girl, who has been trained by her father in the art of self-protection and who is the master of an astonishing array of weaponry, including butterfly knives and taser guns.
Directed by Matthew Vaughn, who also co-wrote the script and with whom Goldman worked before on Stardust, Kick-Ass is based on the eponymous superhero adventure penned by the Scottish comic book writer Mark Millar. The film is shot through with Tarantino-esque action sequences but also manages to be extremely funny, despite the fact that the subject-matter – a pre-teen girl who swears like a sailor and shoots baddies dead with big guns – is somewhat problematic. Seven American film studios turned down the script before Vaughn released it through his own production company.
"We just really wanted Hit-Girl to be a character who, in a sense, simply happens to be an 11-year-old girl, in the same way that Ripley in Alien could have been a guy but the part happened to be played by Sigourney Weaver," explains Goldman. "She [Hit-Girl] is genuinely dangerous, she's genuinely mad. It's not her fault: she's been raised in this environment where she doesn't know anything different. She's unwittingly part of a folie a deux."
Does she think of Hit-Girl, who is played by the 13-year-old actress Chloe Moretz, as a sort of hardcore mini-feminist, a challenge to the usual assumption that most movie violence is carried out by adult men? "Yeah... she's a feminist hero by token of the fact that she pays no attention to gender stereotypes. I think she also doesn't want special treatment because she's a girl."
The film caused controversy in the United States because of a violent online trailer that could have been viewed by children (even though it was clearly marked as "red band", denoting adult content). In the UK, Kick-Ass will be released with a 15-certificate but there is an argument that because the film's protagonists are youngsters, it will prove more appealing to those in the same age group. "You could say the same of Fish Tank, which has swearing and extreme emotional portrayals of violence," counters Goldman. "Kick-Ass is a film for adults. It was never, ever aimed at children."
Will Goldman be allowing her own children – Betty Kitten, 18, Harvey Kirby, 16, or Honey Kinny, 13 – to see it? "The two oldest will see it. My youngest daughter… I have to think about it. I think it's a different deal if you've been on set and known the people involved and you know it's not real. Yeah, maybe.
"You very much see the consequences of violence in the film. I think that films that could be said to glamorise violence are ones where there isn't a physical or emotional consequence, where you have people fire off rounds and everyone is dying off cleanly and it doesn't matter, whereas here, people are bereaved, people are hospitalised, it's kind of unpleasant.
"I really don't think anyone having seen this film would come out of it feeling bloodthirsty… I don't think there's any reliable data proving any correlation between violence and films."
But was Goldman worried about the effects on Moretz, who, despite starring in the film, is too young to go and see it in the cinema? She thinks about this for a moment, hesitating as if to get her thoughts in order. "The fact that she's actually enacting the violence is in many ways probably less traumatic for a child actor than a lot of films where the children are victims of violence – serious films where they're the victims of violence at the hands of family members. I think actually, emotionally, that's a lot more disturbing for a child actor whereas this is comic book; it's light. I don't think it raises any difficult emotional issues for a child to process."
Still, the Daily Mail is in a predictable tizz about it all. A few days before we meet, the newspaper runs an article headlined "Jonathan Ross's wife causes outrage", as though she had been caught mugging Andrew Sachs on the street for his bus pass. Does she care about this kind of press coverage?
"People's intolerance, I find puzzling," she says, a vertical crinkle appearing between her eyes. "The fact that I was singled out, I found bizarre but it didn't upset me, I just thought it was peculiar. It's funny – it's very rare that a movie is described as a writer's movie. It was kind of ironic that it was only when people had decided there was something negative about it that it was the writer's movie… Maybe it's that it makes a good tag on to this ongoing narrative in the press involving other people in my family – it makes it part of that saga."
That is as close as Goldman gets to mentioning the Jonathan Ross-shaped elephant in the room, and it must be frustrating to be constantly pigeonholed as someone's wife when she has been quietly pursuing a successful career as a writer for the last 20 years. Goldman grew up in north London, the only child of liberal, wealthy parents. Like Hit-Girl, she was terrifyingly precocious – leaving school at 16 with eight O-Levels before being hired as a showbusiness reporter on a casual basis by the Daily Star.
A year later she met Ross at a nightclub while working for the paper, and the couple got married when she was 18. Goldman spent most of her 20s having babies but also found the time to write several books (including a novel, Dreamworld), front a television series investigating the paranormal, and cultivate a growing reputation as a screenwriter. As well as her work with Matthew Vaughn, she has just completed the script for a forthcoming film adaptation of Susan Hill's ghost story The Woman in Black. She seems to be intrigued by the supernatural and fantastical and admits to a "geeky" enthusiasm for comic books and computer games.
"I play World of Warcraft, which means I end up hanging out with teenage boys a lot," she says. "I really enjoy the company of my kids… I'm not one of those people who goes 'Yeah, my kids are my mates', that's a dreadful kind of mother, but I'm fortunate that there are times that they do want me around, and I feel lucky that they let me into their world."
There is a part of Goldman that seems to connect easily with childhood, perhaps because she missed out on so much of it herself. "Yeah, I never hung out in parks and got drunk… I never did the proper teenage stuff and maybe that's why it still holds a fascination for me but I like to think it's because I really like that unbiased outlook on life. Teenagers come to things fresh and can really teach us an awful lot.
"I've yet to meet a bitter teenager. Bitterness, jealousy and jadedness, I think, are the most unattractive qualities in a person, and unfortunately they do seem to come with age."
In person, Goldman seems to embody both this freshness and a sort of gentleness that is strangely at odds with her love of violent video games and her striking physical appearance. She has a beautiful face, fire-red engine hair (re-coloured every three to four weeks) and a figure that looks as though it has been drawn by a lascivious comic book artist. Is it a coincidence that she looks like the superheroes she has written about? "That's a huge compliment, thank you," she says. "I've always loved science fiction, fantasy, manga, comic books, so I guess to some degree those things influence my personal idea of what looks nice, which definitely isn't everyone else's."
She laughs, but it must take a certain degree of chutzpah to look so flagrantly individual. "In some way it's less courageous because it's essentially saying, 'I've opted out'; it's saying 'Please don't judge me against society's standards! I know I don't measure up, I've opted out, I'm playing a different game.'"
It is a game that she plays extremely well – but then, all that time practising on World of Warcraft must surely help.
Kick Ass opens on Friday