By Holly Rubenstein and Marie-Louise Gumuchian

LONDON (Reuters) - Oscar winner Renee Zellweger puts on her British accent again to play bumbling Londoner Bridget Jones in the third instalment of the film franchise, with the much-loved character, now in her 40s, single again but unexpectedly pregnant.

The Texas-born actress reprises the role of the weight and love-obsessed character for "Bridget Jones's Baby", with Colin Firth back as the reserved Mark Darcy and new addition "Grey's Anatomy" actor Patrick Dempsey as her love interests.

Zellweger first took on the role in 2001's "Bridget Jones's Diary" and "Bridget Jones: The Edge of Reason" in 2004, both based on the 1990s novels by Helen Fielding.

While now older and working as a television news producer, Jones, described by Zellweger as "a character that I love", still gets up to plenty of mishaps.

"She's familiar to me," Zellweger told Reuters in an interview. "But it was a different kind of experience creatively to figure out how you show that a person has evolved but at the same time not betray the essence of who they are".

The movie begins with Jones turning 43 and single following her break up with long-term love interest Darcy.

But after an encounter with him as well as meeting American Jack Qwant, played by Dempsey, Jones becomes pregnant and is uncertain who the baby's father is.

"She's less naive, I think, which is great that both of her ... suitors are great guys so it's a different sort of rivalry because I think she would be less apt to fall for the silly guy at this stage in her life," Zellweger said.

The movie has been highly-anticipated by fans, who were left shocked with 2013's "Bridget Jones: Mad About the Boy" book in which Fielding killed off Darcy and portrayed Jones a widowed mother with a toy boy.

"From when we started production I've been very nervous about the pressure for it to succeed and whether it would be funny and whether it would work and whether she's still relevant," director Sharon Maguire told Reuters.

"But I think...there's an enduring love for this character."

Asked if she would be open to taking Jones' story further forward, Fielding, also a screenwriter for the movie, told Reuters at the film's Monday premiere: "I would never say never."

"It has to have integrity so I would only write a Bridget story if I had a story to tell and something important to say."

Firth added his interest in making another film should the opportunity arise, saying: "If I'm invited, yes."

"A certain generation is growing up with her (Jones) and some are just discovering her and it will be interesting to see what at the very end will be the legacy of all that," Dempsey added.

(Writing by Marie-Louise Gumuchian; editing by Jeremy Gaunt and Diane Craft)