"Women make the best spies,” contends the actress Isla Fisher, who plays one herself – actually a suburban housewife with a penchant for espionage – in her latest comedy, Keeping Up with the Joneses.

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“I’ve heard that the best Mossad and CIA spies are women,” says Fisher, discussing the subject during a break on the Atlanta set of the stylish caper she describes as “a cross between Mr & Mrs Smith and Spy (last year’s Melissa McCarthy hit)” with a nod to Hitchcock’s Rear Window. “The key to being a good spy is listening. Women make better listeners then men – sorry to generalise – and are more gifted at multi-tasking: a much-needed spy skill,” smiles the Australian star of Wedding Crashers, The Great Gatsby and Now You See Me, who is married to Sacha Baron Cohen.

From director Greg Mottola (Superbad), the film sees Fisher play the astute Karen Gaffney, a “mother caught up in the carpool grind”, married to the gullible Jeff, an HR exec, played by the reliably funny Zach Galifianakis (The Hangover films and Birdman). The Gaffneys have a couple of kids and lead a contented but dull life on a cul-de-sac. Life livens up when the mysterious and glamorous Joneses, (Mad Men’s Jon Hamm and Gal Gadot, the new Wonder Woman and a former Miss Israel) move in next door.

“The genetically blessed Joneses are perfect in every sense – the proverbial ‘Joneses’,” says Fisher. It rapidly emerges that the couple, purporting to be a travel writer and food blogger respectively, are in fact spies. Soon the Gaffneys are swept up in a high-stakes operation, involving car chases, shoot-outs, and face-offs with deadly assassins, for which they are ill prepared.

The scene they’re shooting today, in a brightly coloured, all-American diner, involves a showdown between the two couples over bacon and eggs. Fisher, 40, looking stylish in a blue checked shirt and cropped trousers insists, “I am totally sexless in this film.”

The redheaded actress recounts one scene featuring the two female leads in a state of undress. “Six weeks after having a baby I had to stand in a bra and knickers next to Miss Israel,” she glances across the diner in the direction of Gadot, dressed to kill (literally) in sprayed-on jeans, boots and a white tank top. “I mean, hello!”

Fisher, who has a nice line in self-deprecation, laughs and rolls her eyes. Adept at slapstick, the film provided her with plenty of opportunities for broad physical comedy. “I get hit by a drugged dart while snooping on the neighbours and go through various stages beginning with denial and euphoria moving into sexual arousal before I finally pass out. It is always a dream to get an impediment of sorts when you are acting.”

“Isla is cute and sexy,” says director Greg Mottola, comparing her to Lucille Ball, “but she’s also funny, fearless and willing to look ridiculous.”

The actress admits that comedy is “where I am the happiest… I love to tap into my inner idiot. It’s addictive, the adrenalin hit of going for a laugh and not knowing whether it will land or not.” Her comic influences? “Aside from my hubby’s stuff, I love Monty Python, Fawlty Towers, Blackadder, The Young Ones – I grew up watching British comedy,” she says, also mentioning Amy Poehler, Tina Fey and Amy Schumer.

Comedy is where I am the happiest… the adrenalin hit of going for a laugh is addictive 

Raised in Perth with her two brothers, Daniel and Edward, the actress’s mother Elspeth Reid, a writer, now runs youth hostels in Athens and an eco-tourism business, ‘The Good Life’, on the Greek island of Syros. Her father, Brian Fisher worked for the UN, then Save The Children. (Fisher is an ambassador for the charity; and together with Baron Cohen donated a total of £750,000 to Save the Children and David Miliband’s International Rescue Committee, for Syrian refugees last year.)

Comedy came easily to Fisher. “When I was young we moved a lot and had a nomadic lifestyle; I went to a different primary school every year. I needed to make friends quickly and an easy way to get people to like you is to make them laugh. I can’t psychoanalyse it,” she says, “but my theory is that I was funny because I had to be adaptable.”

Her parents, originally Scottish, divorced when Fisher was nine. Working professionally in her teens, she landed a role on the soap, Home and Away, “a great place to hone my skills. All actors should be able to deliver bad dialogue and have stamina. You are shooting up to ten scenes a day.”

She studied mime in Paris, before moving to LA, appearing in a succession of hit films such as Scooby Doo (2001) and memorably making her name as a sex-obsessed bridesmaid in the raucous 2005 romcom Wedding Crashers.

In Confessions of a Shopaholic (2009), Fisher played a profligate financial journalist. Did she learn anything about investment? “I think the question should be: Did I learn to be financially reckless? I am not a method actor. But I did learn how to count up to 60.”

As we talk, children are racing around the diner. Greg Mottola is unperturbed. Lacking any semblance of self-importance or pretension, the filmmaker has created a relaxed atmosphere in Atlanta: he’s brought his own family along on location, encouraging his leading actors to do the same. Galifianakis and Gadot have their spouses and offspring in tow. Fisher has brought along her daughters, Olive, eight, and Elula, six and her (then) four month-old son, Monty. I am introduced to the actress’s husband, the man himself rather than his alter egos. (Baron Cohen invariably conducts his own interviews in character, as Ali G, Borat and Brüno, etc). Jon Hamm doesn’t have children, “but he used to teach and is brilliant with the kids,” says Fisher.

Recently, Fisher has been concentrating on motherhood rather than her Hollywood career: “I am happy doing one film a year,” she says. Mottola’s child-friendly set was one reason she signed on for this project. “My whole family is here, which is a miracle.” There was also the fact that great roles are hard to come by. “Listen, it’s not as if I get offered the kind of groundbreaking female character roles that would light up my creativity and fire up my artistic sensibility,” she adds with disarming frankness. “I’m sure there’s a litany of other actresses in the same position as me.”

Called back to work, Fisher promises to continue our conversation. True to her word, several months later we meet again, this time at the café upstairs at Waterstones in Hampstead. (The Fisher/Baron Cohens split their time between LA and London.) There’s no trace of the suburban housewife I encountered in Atlanta; today, she’s all Brigitte Bardot-chic in a short, off-the-shoulder number.

Ordering lattes, we discuss recent good reads – she’s immersed in Thinking, Fast and Slow from Nobel prize winner Daniel Kahnhmen, and has just read Elena Ferrante’s bestseller, My Brilliant Friend (the first of the engrossing ‘Neapolitan Novels’). “I’m a bookworm. I used to knock out a couple books a week when I didn’t have so many demands,” says Fisher, who penned two young adult books as a teenager, together with her mother, and recently wrote a well-reviewed children’s book, Marge In Charge, the first in a series.

We wander over to the cookery section. “I love cooking,” she says. “I am really into Gordon Ramsay and Yotam Ottolenghi, but you need the time out to do his recipes.”

The actress lights up, talking about the “normal” pleasures of family life. It’s hard to imagine, though, that life with Baron Cohen is normal. Earlier in their relationship, when Baron Cohen was engaged in guerrilla-style filmmaking for the anti-Semitic, misogynistic Borat, life was a bit different: “Instead of asking: ‘Are you going to pick up the dry cleaning?’ I’d ask, ‘Are we getting sued by somebody?’ or ‘Is there a warrant out for your arrest?’ But luckily when he started to make fictional films like The Dictator, we didn’t have to have those kinds of conversations, because there were no legal implications.”

Working with her husband for the first time, Fisher took a supporting role in last year’s outrageous comedy, Grimsby, which starred Baron Cohen as Nobby, a loutish football hooligan, along with Penelope Cruz and Mark Strong. “He gave Penelope a bigger better trailer than me, which I would tease him about,” says Fisher. “He did an amazing impromptu Michael Jackson dance as Nobby, his trousers seamlessly fell down while he was moonwalking. I ruined so many takes laughing. I was just blown away by how brilliant he is. #braggingwife, I get it.”

Any amusing moments behind the scenes? “My dad and stepmum flew out to Cape Town [where it was being filmed], as they really wanted to see Sacha working, but I neglected to check the call sheet. I took them over to set and all I could see were two animatronic elephants surrounded by the film crew. We got closer, and we couldn’t see Sacha anywhere. Then suddenly, my husband popped his head out of the elephant’s vagina and proceeded to fight against the other elephant’s erect penis. I saw my stepmum’s face – and my mouth was just opening and closing like a goldfish, but no words could come out.”

I would love to work with Sacha again, but not on anything that wasn’t staged. It’s too dangerous 

A great raconteur, Fisher is funny and quick with the one-liners, but admits that her husband is “much, much funnier”. Does the 44-year-old writer and actor bring his characters home? “No, thank goodness,” she says, “only visually. I’ll see a handlebar moustache when he’s doing Borat, or he’ll have the blonde streaks from Brüno, his gay fashionista character. Once, Sacha came back from work while he was shooting Brüno and he had red welts and blood all over his back, and his thumb was broken. It was the result of a scene with a real six-foot-four dominatrix who had tried to force him to have sex with her. When I asked him what had happened, he just said it was a ‘workplace injury’.”

“I would love to work with Sacha again,” she says, “but not on anything that wasn’t staged. It’s too dangerous. I wouldn’t want my thumb broken for my art.”

Fisher was, however, prepared to take on some seriously challenging material for the sake of her art, in the chilling new thriller, Nocturnal Animals, from acclaimed filmmaker and fashion designer Tom Ford – his first since A Single Man. She has a notable supporting role in the film, winner of the Jury Grand Prize at this year’s Venice Film Festival. It stars Amy Adams as an art gallery owner, who receives a manuscript from her ex-husband (Jake Gyllenhaal) – and turns into a brutal revenge piece.

The plot comes to life in her mind and on screen, with Fisher playing Gyllenhaal’s current (fictional) wife. “I’m a suburban Texan mother with a 16-year-old daughter and we are travelling across the desert to our home, when we meet some unsavoury folk. Unfortunately, something happens to me…” says Fisher describing her director as “witty and clever. He’s patient, kind and even at 4am on a night shoot, looks like a rugged runway model,” she laughs. “Everyone who works with him falls in love with him – and that’s not just because they want some free clothes!”

There are no new films on the horizon, though Fisher remains committed to her career: “I love acting,” she says. “It’s the greatest form of escapism.” Clearly content with life, she tells me about her interests beyond cinema and family. An art lover, “obsessed with [late British artist] Beryl Cook, for my 40th birthday my husband bought me one of her works; I was blown away. I have a [picture by] Damien Hirst – a shark and a butterfly. He drew it on the back of an envelope at a dinner party; I was sitting next to him, not realising he was one of the world’s highest-paid artists. I asked him to prove it, so he drew something for me and I framed it.”

She also has a passion for interior design, “making a house beautiful, I don’t know how good I am at it, but I love it. Our house is mid-century modern,” she says, “I love Hans Wegner chairs, Florence Knoll credenzas.” An admirer of the French designer Christian Liagre and Cuba’s Waldo Fernandez, “I subscribe to 1stdibs and a zillion other furniture websites,” she says. “I love antiques, my dad used to collect them. Whenever I have a deadline, I panic and avoid it by going onto a furniture website. I like streamlined shapes,” she says. “Think Loaf mixed with Ikea.”

Ikea. Really? “Yes, they’ve got great stuff. You want a home; I never want to be that person who says, ‘don’t put your feet up on the sofa, don’t put your coffee mug there,’” she says explaining her appreciation for the brand. “You know, it’s very Australian. You come into a home and you just dishevel. In LA some people treat their houses like a show-home, but I’m a bit more ‘live and let live.’”

Fisher and Baron Cohen have been together for 15 years. What secrets she can share about her long-lasting marriage? “Communication is important and having a date night. It is really easy to have a kid-oriented marriage, so just one night a week we try to go out,” she says. A recent evening out was spent at the theatre, watching (The Social Network star) Jesse Eisenberg’s impressive West End debut in The Spoils.

Date nights aside, Fisher likes to “catch up with friends,” including fellow Australian actress, Naomi Watts “and the rest of the koala mafia,” but says “there isn’t much time for socialising. To be honest, I get up every morning between 5.30am and 6am, I take a multivitamin and tell myself, ‘don’t worry Isla, you’re still cool, you’ll go out one day…’ but instead, at the end of the day, I just fall asleep!”

Keeping Up with the Joneses is out on 21 October. Nocturnal Animals is out on 4 November.