EVERYONE feels like they're Jennifer Aniston's best friend. After years of watching her as Rachel Green on Friends, it's as though you know everything about her.

So maybe that's why some people think they can ask intimate details about her personal life and then seem surprised when she's not so keen to answer them.

After being kept waiting almost two hours for our little chat, I'm starting to think "some friend", but Jennifer greets me warmly and instantly puts me at ease.

The 41-year-old's latest film, The Switch, sees her star as Kassie, a successful single woman who gets to a certain age, decides she wants to become a mother but is sick of waiting for Mr Right. So she opts for artificial insemination.

The bizarre twist comes when her best friend Wally gets drunk at her 'insemination party' and spills her specially selected donor's 'sample', so replaces it with his own, thereby fathering her child. And thus the latest romcom scenario is born, quite literally.

Aniston is also an executive producer on the film and clearly it's a subject she feels quite passionate about.

"I jumped at it," she enthuses. "So many women are making this decision in life and taking this discussion out of the taboo category and making it into a celebration. So many of my own girlfriends have gone through it and I just think it's great."

Aniston is adamant it should not be taboo for women to choose to become mothers on their own, as she believes you don't need men to start a family.

"I think there's still a group of really ignorant people that say it's because these women have failed at something. They 'failed' at obtaining the ideal of the picture-perfect family. I just don't think that's fair.

"Sometimes you're ready and you're just not going to wait 'til somebody comes along who you don't really want to spend the rest of your life with, you know?"

In her own personal life, Aniston hasn't had it easy.

She's constantly been at the centre of the rumour mill since ex-husband Brad Pitt fell for Angelina Jolie, during filming on Mr And Mrs Smith, while still married to Aniston.

But then her film choices have also caused people to speculate that art might be imitating life.

After the split with Pitt, her next big movie was called The Break-Up, where she started dating her co-star Vince Vaughn - and then they broke up.

She went on to star in a string of romantic comedies, as gossip magazines followed her dating life with avid interest, portraying her as the lonely, childless single woman, while Brad and Angelina built up their family.

And then there's The Switch, about a single woman who decides to take matters into her own hands to become a mother, before it's too late.

So was the 41-year-old star bothered about the speculation overdrive the film would incur as to whether she's considering the same thing?

"Well, no," sniffs Jen. "The media create stuff that's not real, so if there's a moment where they can match a tabloid headline of 'pregnancy' to me, then of course I don't think that's a moment anybody would miss."

So does she have a life plan like Kassie?

"Obviously not," she laughs, slightly tersely. "I'm just sticking to my plan, which is: wake up in the morning and be as happy as you can be... and live in gratitude."

There's a hint of Aniston's maternal side when she talks about child actor Thomas Robinson, who plays Kassie's awkward, neurotic son Sebastian in the film. She describes him as "delightful", then confesses she worried about him working past his bedtime.

"Thomas is just so little. I mean half the time I was just going 'Oh my God, shouldn't you be in bed?!'

"This business is just hard, the hours are long, he's so young but," she laughs, "you need a kid in a movie, so what are you gonna do?!"

Aniston was always destined for showbiz. Born in Sherman Oaks, Los Angeles, California to actor parents, her family moved to New York where she studied acting and appeared in off-Broadway productions, supporting herself by doing part-time jobs including waitressing.

Jen moved back to Los Angeles in 1989 but, after a string of parts in failed TV shows, considered giving up acting until she was cast as Rachel Green in hit sitcom Friends which ran from 1994 until 2004. The 'Rachel cut' became a sensation in hairdressing salons around the world - and millions tuned in to see her finally get together with Ross (David Schwimmer).

Arguably the most successful of the cast post-Friends, she's branched out this year and just launched her own perfume at Harrods, simply called Jennifer Aniston.

The posters advertising the scent show off her toned and slender figure on the beach.

Aniston, who has a pizza oven in her California home, insists the secret to her looks is an occasional indulgence: "You have to indulge, but that's why you've got to do a run and balance it out. It's all about the balance."

For all the romcoms she's starred in, Aniston is a pragmatist at heart. She likes the love story in the film between best friends Kassie and Wally, played by Jason Bateman, because it's true to real life.

"I don't think Kassie has a realistic idea of what that perfect person is," she explains.

"I think it's why she decides, 'That perfect person isn't going to come along so I'll create the perfect child by getting the perfect donor' - but she's missing this wonderful person that's right in front of her.

"What is perfection anyway?" scoffs the ex-wife of Brad Pitt. "You don't know what shape or physical form love is going to come in."