By Tom Bishop
BBC News entertainment reporter
Renee Zellweger earned an Oscar nomination for her starring role in Bridget Jones' Diary.
Zellweger has won an Oscar since first starring as Bridget Jones
But the actress has said her involvement in sequel The Edge of Reason was no foregone conclusion.
Since gaining widespread attention in the original Bridget Jones film (2001), Zellweger's roles have included an acclaimed performance in Chicago and an Oscar-winning turn as Ruby Thewes in Cold Mountain.
"I was working on Chicago in Toronto when people started to approach me and ask whether I was going to do a second Bridget Jones movie," the actress told a press conference for the film.
"People's enthusiasm about the idea started to make me wonder if it might be worthwhile."
Paradoxically, the lean Texan's previous success as the wine-loving, weight-obsessed English thirtysomething Jones made her hesitant to reprise the role.
"It is a privilege to play a character like Bridget Jones," Zellweger said. "It is not martyrdom to change your body a little bit to play a character that you love.
"My fear came from being really scared to do something that might compromise how people felt about this character, to be part of something that might disappoint people."
Zellweger stars alongside Colin Firth and Hugh Grant (right)
Nevertheless when Colin Firth and Hugh Grant once again signed up to play Mark Darcy and Daniel Cleaver respectively, Zellweger accepted the role.
Director Beeban Kidron added: "If the three principal actors had not been there, there would have been no Edge of Reason."
The "acknowledged nervousness" of the romantic comedy's cast and crew was "completely healthy", Kidron added.
"Renee in particular felt she had a lot in her hands - the hearts of all those people who fell in love with her in that role."
Set four weeks after the first film, the Edge of Reason sees the heroine become depressed and uncomfortable with her previously hard-won partner Darcy.
Budding TV presenter Jones finds herself embarking on a slapstick ski-ing trip to Austria and an ill-fated trip to Thailand with the untrustworthy Cleaver.
Zellweger said she saw Jones as endearingly insecure rather than slightly pathetic.
"The film is about this woman whose humanity and honesty is appealing, something we can recognise in ourselves," she said.
"It did not need to be desperate. She is not someone who is disheartened about her own feelings or self-pitying."
The film includes a cameo by BBC Two's Newsnight presenter Jeremy Paxman, whom Zellweger described as "very charismatic".
"He said he had gathered the whole of the world's news in the time it took us to shoot that scene," said Kidron.
In another section Jones leads a group of Thai prisoners in a mimed performance of Like a Virgin by Madonna, who has yet to see the film.
"Madonna is someone with a great sense of humour about herself," said Kidron. "I am sure she won't be silent if she doesn't like it."
Zellweger attended the film's world premiere in Sydney in October
Zellweger plans to take a break from acting after completing current projects The Cinderella Man, about Depression-era boxer Jim Braddock, and Janis Joplin biopic Piece of My Heart.
"A lot of projects I had been following for a long time seemed to have all surfaced at once," she told reporters.
"I have never felt that drive to keep going and going until I achieve something that I can feel comfortable with.
"Most of the experiences I have had over the last seven years have been while imitating someone else.
"I need to find out as a woman now what I would do each day, and what I would learn, having not promised that day away for professional objectives."