SHADING herself from the Mediterranean sun, Emily Mortimer talks at a breathless clip, gently self-mocking, eager to please. A willowy beauty with a decade of screen roles behind her and a rising profile in Hollywood, the 33-year-old actress is visibly jittery after leaving her baby son Sam for the first time in eight months to make a brief promotional trip to the French Riviera. Mortimer is prim politeness personified, but clearly distracted by the surging hormones of early motherhood.

“The whole work thing is hard,” she frowns. “The whole of the rest of life is difficult because you feel such love and such guilt. Guilt is one of the primary defining emotions of parenthood, I’ve discovered. You start feeling guilty about sitting here . . . but I guess that will stop.”

Coincidentally, Mortimer stars as a guilt-racked young mother in her latest film, Dear Frankie. The writer-director Shona Auerbach’s whimsical Scottish fable is small in scope and ambition but handsomely shot and potentially sugary enough to reel in the Billy Elliot crowd. Despite spending most of the year in Los Angeles with her American husband, the actor Alessandro Nivola, Mortimer seized the chance to make yet another of the low-budget British features that mostly have defined her career to date.

“I needed a job,” she says. “And also any excuse to do a job in the British Isles. I’m spending quite a lot of time in America because my husband’s there, so I would come home at the drop of a hat.”

Dear Frankie marks Mortimer’s second Scottish accent in quick succession, after her sexually graphic turn as Ewan McGregor’s doomed beatnik lover in David Mackenzie’s critically acclaimed drama, Young Adam. She insists that adopting a voice very different from her own is an easy short cut to inhabiting a character, although she is careful to differentiate the subtle social shadings that define each role.

“I’d done it before in Young Adam,” she says, “but she was actually quite a middle-class girl, a pseudo-bohemian who liked smoking cigarettes and sitting in pubs and talking about poetry. But she probably was a nice conventional girl really. And this girl isn’t; she’s from a working-class background and probably hasn’t been very well educated, although there’s an innate intelligence about her.”

Accents are a moot point here. Having settled in Los Angeles, swapping the elegant English Rose image of her Notting Hill cameo for the Americanised twang of Scream 3 and Lovely and Amazing, Mortimer could easily have followed the well-trodden Catherine-Zeta-Bonham-Carter-Hurley path to Hollywood accessibility.

Instead she still sports frightfully clipped English vowels, deploying charmingly antique turns of phrase such as “not quite the ticket” and “nincompoop” which sound more Jeeves and Wooster than Sunset and Vine. No wonder Stephen Fry cast her as a ditzy 1930s flapper in Bright Young Things, although he likened her quick-witted off-screen self to Emma Thompson.

Educated at the posh St Paul’s Girls’ School in Southwest London, then Lincoln College, Oxford, Mortimer once described herself as “a Sloane from the Chilterns” with tongue only slightly in cheek. Alas, the patina of irony faded over the years while the quotable soundbite endured.

“You have to be very, very careful,” she sighs. “Let’s not revisit that quote. It’s terrible!”

Mortimer actually does a credible impression of a dizzy Sloane, rushing headlong into open-ended sentences that scamper around in giddy circles before imploding like a soggy picnic hamper in a summer storm. But behind this apparent insecurity, or calculated modesty, she plainly has brains to spare. She is fluent in Russian, wrote a Bridget Jones-style newspaper column in her mid-twenties, and has already written her first screenplay, an adaptation of Lorna Sage’s memoir Bad Blood, which, she admits, almost drove her mad.

“If I’d known when I’d embarked on writing it what a tortuous process it was to get a film made, I would probably never have done it,” she says. “It sent me out of my mind at the time. I decided I was going bald in a moment of insanity because it was easier to examine my hairline three times a day than to sit down and write this f****** thing. But very satisfying when you finally do it, although it’s never finally done.

“They say it’s going to happen this year; they’ve announced it and everything. But until it starts, I don’t believe it.”

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