It's hardly a novel predicament for Fitzgerald. For large chunks of her bodice-ripping career in TV costume dramas she seemed to strip for England. But this latest seduction of a young man half her scripted age makes you acutely aware how grown-up she has become.
The 34-year-old is still improbably sexy, with huge brown eyes, cheekbones that wouldn't look out of place on a bone china mug, a cut-glass accent and hair you could pour out of a shampoo bottle. She's also great company: as passionate about the remarkable background to her new film as she is modest about her contribution.
Sverak has freighted Dark Blue World with a revelation about the Czech contribution to the war effort that makes the blood run cold. Shortly after their return home, the pilots who served with the British were rounded up and interned in the most ghastly labour camps by the Soviets lest they contaminate their fellow citizens with ideas of democracy.
"I was appalled by that fact," says Fitzgerald. "These Czech pilots were denied the freedom they fought for. I met some of the veterans in Prague when the film opened - lovely, saucy men - and remarkably they had no bitterness about it at all. But they were worried about the film. For them it's a can of worms. They feel terrible guilt and responsibility about the history they lost and the things that were 'disappeared'."
It certainly takes Sverak's film out of the rose-tinted nostalgia so crudely churned out by legions of Second World War romances. In the Czech Republic Dark Blue World has smashed domestic box-office records, outstripping Titanic by several hundred icebergs.
That the romance holds so well in a story that's narrated from the grim confines of a Soviet prison block in the 1950s is in no small part due to Fitzgerald's magnetic input. Having relieved young Krystof Hadek (ironically hailed by the Czechs as the new Leonardo DiCaprio) of his virginity, she unexpectedly falls for his mentor and father figure, Ondrej Vetchy.
"My feeling is that life is unfortunately like that," muses Fitzgerald as she lights a cigarette. "You get shafted in the derriere when you're really not looking. War profoundly changes the way people behave. It makes you aware of solitude - mortality - in ways perhaps you were not aware of before.
"You can't really research those things. As an actor you have to make a leap of faith. The only thing that came close for me was watching the events of 9/11 from across the water in Brooklyn. You suddenly felt what it was like to be in an extraordinary situation. Manhattan was a war zone. Everybody was confused. But people were incredible in how they reacted. Firefighters became national heroes. The Czech pilots who fought the Nazis were denied that, and by their own people."
The Fitzgeralds have no war medals in the family chest. But they're not short of the odd artist and actor. Sarah Fitzgerald, Tara's Irish mother, is a portrait photographer. Her stepfather, Norman Rodway, who died last year, was an RSC stalwart. Her cousin, Jennifer Johnston, is a novelist. And her great aunt, Geraldine Fitzgerald, acted with Laurence Olivier in Wuthering Heights (1939).
Her real father, an Italian-born artist, Michael Callaby, died tragically when Tara was 11. Suffering bouts of black depression, he committed suicide. A detail that Fitzgerald wasn't told until she was 19. That, and an ectopic pregnancy, understandably made her first year at the Drama Centre in London less than delirious.
Trauma, like stardom, does strange things to people, but it rarely makes them sane. Fitzgerald is a sparkling exception. After graduating, she landed a part in Peter Chelsom's maudlin film Hear My Song (1991), which won rave reviews.
Beefy television roles, notably The Camomile Lawn, followed. Then media hell seemed to break loose. In the 1990s, she headed the shortlist of British temptresses who could do no wrong. Her abhorrence of political correctness was as refreshing as her carefree attitude to nudity. It helped her secure roles opposite some of the most glamorous squeezes to be had on screen and stage, including Ewan McGregor in Brassed Off, Hugh Grant in Sirens and an award-winning turn as Ophelia to Ralph Fiennes's Hamlet.
Yet unlike her fellow sexpots - Helena Bonham Carter, Catherine Zeta-Jones, Kate Winslet, Rachel Weisz and Kate Beckinsale - Fitzgerald has never quite cut the mustard in Hollywood and I'm not sure why. "I had an obsession as a child that I would live the Hollywood life," she says. "And then it just didn't happen."
Projects were offered, but nothing fitted. "You have to have a particular personality to go out there and scratch around - unless you're really lucky. Even then I think they come and find you. That might be naive reasoning, but Kate Winslet and Rachel Weisz were both cast for big films on these shores so they probably knew what they were looking for."
Has it been a source of frustration? "Hollywood does give you a springboard. I read that after doing The Mummy, Rachel can pretty much do more or less what she wants. In that respect it gives you a sort of freedom. But you need to find the right vehicle. She was perfect casting for The Mummy. I'd need to find an equally true part for me to do - if that doesn't sound too worthy."
Despite the odd homegrown stinker (the thriller Rancid Aluminium, for one), the Europeans love her. In the past year she has made two more films yet to be released: I Capture the Castle, based on a Dodie Smith novel; and Secret Passage, about the Spanish Inquisition and the Jewish Diaspora to Istanbul, which has her wheedling out the secret of Venetian glass-making from an Italian noble (played by John Turturro).
The appetite for endless television sagas has dried up somewhat but Fitzgerald has other concerns. She's married to the actor John Sharion, whom she memorably played opposite as Blanche to his Stanley in a dynamic production of A Streetcar Named Desire at the Bristol Old Vic. Now there are babies to think about. Or maybe not.
"I don't know," she confesses. "I'd like it if it just sort of happened. I don't know if it can sort of happen. (She lost a fallopian tube in the ectopic pregnancy.) Were I to have a baby, I'm the kind of person who would go, 'Right, that's it. I want to be with my child'. Enough of my friends and sisters have kids for me to know it's devotional. But it's best not to think about it too much. That's the truth of it."
The older, wiser Fitzgerald knows the truth only hurts those that fear it.
