Peering into her monitor, Gurinder Chadha watches as a four-year-old girl casually drapes another strand of spaghetti over the head of a fluffy, grey cat. The harassed-looking teenager beside them huffs in exasperation at her young sister’s handiwork.

The moggie seems remarkably unfazed and Chadha gives a contented chuckle. “Cut,” she calls. “Let’s go again, and Georgia, this time try an even wearier sigh.”

The Georgia in question is both the young actress Georgia Groome, last seen in Paul Andrews Williams’s harrowing drama London to Brighton, and her character Georgia Nicolson, star of Angus, Thongs and Perfect Snogging, the first in the bestselling teenage novel series from the author Louise Rennison.

Rennison’s comedic Confessions of Georgia Nicolson books may not yet have the renown of Adrian Mole or Bridget Jones, but the fictional diaries are wildly popular with teenage girls on both sides of the Atlantic. Their heroine and her tribulations with an ever-embarrassing family, dating disasters, semi-feral cat Angus and quirky slang – “nunga-nungas” (breasts) are signals to “gorgey” (gorgeous) or “marvy” (marvellous) “Sex God” boys – have become an inspiration for hapless adolescents everywhere.

Big enough business, in fact, for Paramount Studios and Nickelodeon to draft in Chadha for Georgia N’s cinematic debut. The bubbly 48-year-old British-Asian film-maker had been attached to the long-planned film version of Dallas. When that project stalled again, directing Angus . . .felt like a natural fit, particularly given the huge success of her previous teenage girl portrayal, Bend it Like Beckham. Yet initially Chadha and her husband/co-writer Paul Mayeda Berges took the gig only as a writing job. “It’s so much about my own school time,” Chadha explains, “and I thought this was an opportunity to make a very culturally specific English movie. And then once I’d finished the script, I kind of liked it so much, I didn’t really want to give it to someone else.”

Combining Rennison’s first two novels into the Angus screenplay, Chadha quickly dispensed with the journal format and, in her words, “turned it into a proper movie” complete with character arcs and a big set-piece party climax (perhaps unsurprisingly, one of Georgia’s “Ace Gang” group of friends is now of Indian descent). When we meet again a few months later at the first preview screening, she admits the film is her homage to Eighties-teen-movie-king John Hughes’s Sixteen Candles. “It’s so charming and funny but it should be also quite moving,” she says of her tribute. “And it could easily end up being any one of those things rather than all three.”

Inevitably, casting Georgia Nicolson was crucial and developed into a long, often frustrating search. In fact 15-year-old Georgia Groome, one of the first actresses Chadha saw, was initially rejected. “She was just too much of a little girl,” Chadha recalls ruefully. “The scenes with her kissing would have been yucky. Then five months later I called her back in and she’d grown up. All of a sudden she had curves. She still came in in a big floppy blouse but her face was different. It’s great because during the course of the film she’s kind of grown up more – especially with the boys around . . . ” Ah, the boys. In the story, Georgia falls for local “Sex God” Robbie, while her best friend Jas, played by Eleanor Tomlinson hooks up with his brother Tom. Cast a film with real teenagers and, given all those fizzing hormones, it’s surely no surprise if life starts to mirror art.

“What have you been told?” giggles Groome between takes. “Nothing’s gone on,” she protests, her fresh face turning a pale shade of cerise when co-star Aaron Johnson’s name is casually mentioned. “He’s just one of those people whom I really get along with and could probably talk to about most things.”

“How wet!” counters her co-star Eleanor Tomlinson mischievously, mock-rolling her eyes when Groome’s remarks are relayed. “I think there was a stage during filming where there was definitely something going on.” A bit too much full-frontal snogging rehearsal, then? “I think so.” Yet when quizzed about her own alleged co-star relationship, Tomlinson demurs with a winsome, equally diplomatic, “We’re just really good friends . . .”

It’s all said with much good-natured teasing and humour. Taking a cue from its warm, inclusive director, a Gurinder Chadha film-set is something of an extended family affair. Within half an hour of arriving, this journalist is sharing her cheese toastie, while Groome and Tomlinson jig about filming the crew on a DV camera and Chadha’s newborn twins arrive for an impromptu photo shoot.

Moreover it gels nicely with the appeal of Rennison’s novels, in which the comedy highlights, such as Georgia accidentally shaving off her eyebrow or attending a fancy-dress party as a stuffed olive, are largely autobiographical. If the author’s own reaction is anything to go by, the many fans of the books will be more than happy.

“I was really scared,” admits Groome. “What if [Louise] meets me and she thinks, ‘No, that’s the wrong girl’? Then one day on set this lady was waving at me and came over and was like, ‘Hi, I’m Louise Rennison. You’re my Georgia.’ And I was like, ‘Wow’. ”

If Chadha can score with her Beckham magic again, the next teenage film franchise – and one predominantly for girls at that – could be born. And both Georgias can agree, that would be pretty marvy.

Angus, Thongs and Perfect Snogging is released on Jul 25 2008

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