On Sunday, the flashbulbs will pop at Brad and George; the pundits shall scrap over the relative merits of Hugo and The Help. And, away from the limelight, Bafta will be quietly making history. For the first time, British women are in contention to win both the best adapted and best original screenplay.

In the former, Bridget O'Connor is up for the Tinker Tailor Soldier Spy script she co-wrote with her husband, Peter Straughan. And in the latter, Abi Morgan, the woman behind The Iron Lady, is battling Kristen Wiig and Annie Mumolo, whose Bridesmaids screenplay is current frontrunner. This year, an unprecedented number of women are vying for writing trophies.

Sadly, O'Connor is also the second woman to be Bafta-nominated posthumously (the first was the costume designer Marit Allen who won for La Vie en Rose in 2008). She died in September 2010, aged 49, five days before Tinker began shooting. Having first battled cancer a decade before, she finished the script while suffering a relapse.

"Bridget's death was shocking," says Tim Bevan, co-chair of production company Working Title, who dedicated the film to her. "I guess it made everyone do their job better. When something like that happens you either all down tools or you think, 'well, we've got to make a brilliant movie'."

O'Connor's involvement – and her gender – was key to the success of the script, says producer Robyn Slovo. "Peter's great skill is structure. Bridget brought lyricism, the grace notes." It was she that came up the scene of Smiley disconsolately swimming on Hampstead Heath to wile away his retirement. She who added the breastfeeding mother that falls victim to a stray bullet during the pre-credits scene.

"Bridget could go off-piste in terms of texture and imagery," says Slovo. "She had a wacky elegance, both in her work and her personality – she was very witty and dry and direct. She brought moments of poetry; and they are kind of feminine qualities. Though that isn't to say Peter doesn't have them too."

O'Connor's legacy is to have further established the role of women writers in British film, particularly in the realm of hard drama, as well as comedy. Abi Morgan is prolifically pushing this envelope, too: this year not only has she scripted The Iron Lady, but also Shame, Steve McQueen's unflinching study of sex addiction in New York. Both Shame and Tinker bear comparison with The Hurt Locker, Kathryn Bigelow's macho study of bomb disposal experts in Iraq, which she co-wrote with partner Mark Boal, and which made her the first female best director Oscar winner in 2010.

"All these films raise questions about what is male," says Morgan. "Shame is about a man going through emotional and physical torment but at its centre it has heart. The Hurt Locker is set in a very masculine world but, again, it was about people in flux. Tinker, too. And it's good to have added female understanding of that."

Morgan credits the rise in female screenwriters partly to the influence of women such as Christine Langan at BBC Film and Tessa Ross at Film4, who actively advocate for other women. "There are more running partners," says Morgan. "You become a part of a constellation. I always feel a sense of a little boost when I look at a great film and see it's written by a woman. Five years ago I'd have struggled to give you names. Now I can keep reaching for them."

A study published by the Institute for Employment Studies in 2006 made for grim reading. Between 1990 and 2005 women represented less than one in 10 of the Bafta screenplay nominees, and just three out of 43 were winners, none British. Measures were proposed: more positive discrimination, along the lines now suggested by Birds Eye View, which lobbies for female film-makers.

What happened was that audiences voted with their feet, stampeding to see a film made, essentially, by women for women. Mamma Mia! is still the UK's most lucrative movie. Scripted by Catherine Johnson from her own musical, directed by Phyllida Lloyd, it was machine-tooled for a market that had rarely been targeted. The female audiences responded by replicating the viewing behaviour of the teenage boy demographic that cinema has traditionally courted hardest, with repeat visits, en masse, and DVD sales later.

The Iron Lady, Lloyd and Meryl Streep's follow up to that film, is wooing a similar crowd. Increasing numbers of British movies are aimed at older women. Look out in a couple of weeks for The Best Exotic Marigold Hotel, an adaptation of Deborah Moggach's novel about a clutch of pensioners, including Judi Dench and Maggie Smith, who decamp to India.

"In sheer numbers," says industry analyst Charles Gant, "the older audience is the biggest, so if you can make a film that engages it, such as The King's Speech, there can be a huge upside. And older women are a much more attractive audience than older men: they tend to be more culturally engaged, sociable and organised. They make plans, usually with friends. In fact, women of any age are much more likely than men to go in a group to the cinema."

In the US, Bridesmaids has borne witness to a similar trend, albeit skewed slightly younger. That film took $288m (£183m) worldwide from a budget of $32m. Its makers benefited from the success of Diablo Cody's debut screenplay, Juno, which took $238m from a $7m budget three years before.

Cody is the current de facto spokesperson for the new wave of female screenwriters. "She's an incredibly funny, powerful, unflinching writer," says Morgan. Cody is the aspirational poster girl for those attending the Athena film festival in New York, which takes place this weekend, and aims to champion "creativity and sisterhood".

Yet the sense this side of the pond is that such campaigning is not necessarily required. "I don't think it's a feminist issue at all," says Ronald Harwood, who picked up the adapted screenplay Bafta for Diving Bell and the Butterfly in the same year Cody won for Juno. "It still might be miserable if you want to be a woman director, but it's never really been the same with screenplays."

The consensus seems to be that internal as much as external change could be key. "Perhaps it's a self-confidence issue," says Slovo. "It's not about women being not as good. Writing is the most lonely job. Maybe women feel the agony of that more acutely."

"I think I'm relatively sex-blind when it comes to writers," says Bevan, though he will admit to a certain bias dependant on the material. "If you've got a Jane Austen you try and get Emma Thompson to write it. For a hard-ass thriller you would instinctively go towards a male writer, although Bridget slightly disproved that with Tinker."

O'Connor's Bafta nomination, then, is a game-changer. The tragedy is that she is unable to share in it. "But there's real delight that Bridget's last piece of work has been seen by so many," says Bevan. "Had we been working on a film that had passed unnoticed I think that would have been a great deal more painful."