What a mouth: “F***ing hell, it’s f***ing you! Look, sorry, I have to go, I’m doing an interview, speak later.” We have barely sat down and Sharon Maguire, the pretty, fidgety, 48-year-old (going on 14) director is already effing and blinding to a friend on the phone.

Of course, this will come as no surprise to a chick-flick fan. As well as directing Bridget Jones’s Diary — her cinematic debut — Maguire was the template for Shazzer, Bridget’s sweary, scary feminist best pal in Helen Fielding’s novel.

Now the director has turned her attentions to Osama bin Laden in Incendiary. Based on a novel by Chris Cleave, it tells the story of a working-class London mother played by Michelle Williams (Brokeback Mountain) who loses her husband and child in a terrorist attack on the Arsenal football stadium. A far cry from rom-com froth, you may think — though there is a bit of rumpy-pumpy with Williams’s suitor, Jasper Black (Ewan McGregor). But, as with Bridget Jones, Incendiary plugs straight into the Zeitgeist: in 2001 it was sexual neurosis, today it’s terrorism.

“It’s about the peculiar, haunted times we live in,” Maguire explains. “Every time we get on the Tube, every time we go to a stadium. Even now someone was saying: ‘Has the economic crisis somehow been caused by al-Qaeda? And, while all our minds are on this, what else is going on?’ ”

Like the lead character, Maguire was a new mother and lived in the shadow of Arsenal’s football ground. Every time her boyfriend, the producer Anand Tucker, headed off to a game she feared that he wouldn’t come back. “I was terrified.”

He nearly didn’t come back on July 7, 2005. That morning he ran to get the No 30 bus. That No 30. But he missed it. Back home, Maguire thought he was dead. “I had to stay with the kid, who was obsessed with the TV and the ambulances. And I was trying to ring Anand but couldn’t get hold of him; the phones were down. So I spent seven hours thinking ‘He’s dead, I’m a widow’.”

Tucker was fine. But the film, which Maguire was already working on, and the novel were in serious jeopardy. The book’s launch date had been July 7. The publisher had to poostpone, and the production company put the movie on hold.

The most inauspicious of beginnings didn’t put Maguire off. She had fought to get the film rights to the book — “With other people interested I got quite competitive, you know, in a I-want-the-last-dress-in-the-shop sort of way” — and the money was still behind it. The financial position, however, was always scary.”

When a million-pound backer pulled out they were forced to make huge cuts to the script to stay afloat. Scenes were shelved. “There are a few plausibility gaps,” Maguire admits. She had been nervous anyway about the script, which was her first attempt to write one from scratch. “I don’t think I got anywhere near where I wanted to. In fact whenever I saw other people’s stuff I felt pretty useless.”

And there were other worries, such as how to stage the stadium attack realistically on a shoestring. And Michelle Williams’s cockney accent. “She was terrified. I was terrified. And, well, I think, maybe, she pulled it off.”

Maguire has an sensitive ear for these things. She knows her accents. She grew up in an Irish family in Coventry, studied at Aberystwyth University, and then settled in London, working in publishing.

After a year on a post-graduate journalism course at City University she landed a plum job as researcher, then director, on Channel 4’s Media Show. She moved to the Late Show, that iconic forerunner of Newsnight Review. She directed four live programmes a week, sleeping at her desk and working “f***ing hard”. She moved on to high-minded BBC Two arts documentaries in the late Nineties. And then came Bridget Jones.

“Helen Fielding said, in the nicest possible way, ‘We can’t get anyone to direct this, there might be a chance for you.’ No one had any idea it would be a hit or they’d never have given me the job.”

In following years publishers flooded Maguire with rom-coms. But she didn’t take the bait — and regrets it. Instead, she asked her agent to find her the opposite. She was sent a manuscript of the unpublished Incendiary. “I didn’t love it,” she says. “I just found it deeply disturbing, in a way that spoke to our times. It was a sort of haunted Kieslowski take on modern times — that makes me sound like such a w****r, doesn’t it?”

She came away thinking that no one would ever shell out any money for it. And though they did, she still doesn’t imagine it’ll get any decent box-office returns. “Will people want to run out and see a film about London being blown up and children killed? I’m not sure.”

In this climate, she thinks, rom-coms are the future. “The news is such a nightmare that rom-coms are going to take off. Everybody’s just going to say, give us a laugh, something to escape from this . . .”

And Incendiary? “OK, a bit of bad timing, perhaps.”

Incendiary will be screened at The Times BFI London Film Festival on Saturday (Odeon West End 2, 6pm) and Sunday (Rio, E8 3.45pm). It is released on Oct 24 2008

Editor's choice

• The 100 Best Films of the Decade
• 70 facts you didn't know about Marvel
• The 50 Biggest Movies Of 2010