From the first tight smile, it’s obvious Sarah Jessica Parker is not planning to do a big screen Carrie Bradshaw in her first movie since leaving Sex & the City behind.

Her character in the film The Family Stone, Meredith, is a controlling, stressed out executive who is reluctant to release her mobile phone or share a room with her boyfriend in his family home.

The comedy drama is driven by Meredith’s uptight personality clashing with the laid-back, politically correct family of her boyfriend Everett Stone, played by Dermot Mulroney, when they visit for the Christmas holidays.

“It was a very hard part because she [Meredith] is complicated and not immediately likeable,” says the very likeable Parker.

“And I didn’t want to make her likeable before I thought it was appropriate to see all her complexities and dimensions and to see how human she was.”

Looking sophisticated in a classic up-do and McQueen dress, Parker is glowing as one would expect a Hollywood actress to do, even when outside London is miserable and rain-sodden.

She is here on a 24-hour visit to promote the movie, written and directed by Thomas Bezucha and co-starring Diane Keaton as the family’s formidable matriarch, Luke Wilson as Mulroney’s slacker brother Ben, and Claire Danes as Meredith’s sister.

Parker is excellent as the girlfriend besieged at first by the family’s bohemian button-pushing behaviour, then slowly unwound by their acceptance.

Anyone who sees the film and then meets Parker will quickly realise that she has more in common with Meredith than she does with Carrie.

While not suggesting Parker shares Meredith’s more uptight behaviour - in fact she is incredibly at ease and relaxed with eight journalists all shoving tape recorders towards her - she is similarly reserved and has a very strong sense of what is right and wrong behaviour.

Later in the evening during an appearance on BBC1’s Tonight with Jonathan Ross that reserve is illustrated further when questioned about her attitude to discussing sex with friends. “That’s not something I’m comfortable doing,” she tells Ross as she giggles nervously.

Fans hoping to find that Parker and Carrie are one will be further disappointed by her calm exterior, although one should imagine for Parker this is somewhat of a relief. Where her Sex & the City character was all manic drama, Parker is far more at ease with her place in the world.

She says she took her time and a lot of guidance when choosing her next role after Carrie and, although she doesn’t exactly say it, the appeal of Meredith must have been her complete contrast to the open, emotional columnist with a shoe obsession.

“I loved the way he [Bezucha] wrote Meredith,” says Parker. “Such a challenging role, she was so different from any woman I know.” Parker has obviously not been hanging out with any uptight, high maintenance ladies of late.

“Tom was really good at reminding me of her physical carriage which suggests so much about her,” she continues. “I move a lot when I talk and Carrie was all [moving her arms around her head] loose. Meredith just doesn’t move, she’s so tight. It was quite exhausting to do all day, but he made it hard in a good way and I, thankfully, think I work best when it’s challenging.”

And challenging is something that Sex & the City ceased to be. Parker had to confront her aversion to change in order to push herself out of the comfort zone of Carrie and co. “It was a very hard decision to end the show, I would have stayed there forever,” she says.

Observers may say that she hasn’t pushed herself that far, given that The Family Stone is a comedy drama. But that’s not how Parker views her role.

“I really don’t think of Meredith as comedic,” she says. “Whatever happens is environmental and circumstantial rather than something like LA Story (she played Steve Martin’s roller skating girlfriend SanDeE) which is classic comedy.”

It is quite feasible that without Carrie, Parker would not have had Meredith. Before, and during, the Sex & the City series she appeared to be typecast in a run of airhead blonde roles in movies such as First Wives Club, in which she co-starred with Keaton, and Honeymoon in Vegas.

Carrie’s rollercoaster life allowed Parker to fully stretch herself, and the fact that her character was so believable in a fantasy life of walk-in designer label filled wardrobes on a newspaper journalist’s wage, is testament to her acting skills.

Parker has recently finished filming the disturbing drama Spinning into Butter about a race-hate crime on a college campus. It will be interesting to see how she handles a hard dramatic part, but as she acknowledges – she works best when challenged.

The Family Stone is on general release from December 16.

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