He has been awake since 5.30am and is now, six hours later, roaring his lines for the 11th time in the marble-columned ballroom of Kedleston Hall in rural Derbyshire. Yet the delivery of his political monologue is flawless. UK actor Simon McBurney is the kind of supporting actor that big-budget productions, such as The Duchess, love.

McBurney plays Charles James Fox, leader of the Whig party and protege of Georgiana Devonshire nee Lady Spencer, played by Keira Knightley. The scene takes place at the beginning of the 17-year-old's marriage to the Duke of Devonshire, played here by Ralph Fiennes. The young beauty, who hardly knows her husband, decides to make the most of her new position, and becomes a shining star of English society, with a salon that gives le ton to the rest of England.

Beauty spot

According to UK producer Gabriella Tana, director Saul Dibbs convinced her he was right for the job thanks to his work on the BBC TV mini-series The Line Of Beauty. Recalling the origins of the $30m (£15.3m) The Duchess project, she says: "I optioned the rights of Amanda Foreman's biography eight years ago and developed a first script to produce with Michael Kuhn. We went through different drafts." The script is written by Jeffrey Hatcher.

"With time, however, we felt the need to reduce the time span and concentrate on the first part of her adult life. The search for a director and cast went on for a long time. Finally, Saul, Keira, Charlotte Rampling and Ralph Fiennes committed to the project. At last we could shoot ... but we almost lost Ralph at the last minute because of his other commitments."

Hairdresser Lou Sheppard checks the powder on the extras' wigs while Fiennes enters the hall wearing a jacket and blue jeans; he sits at the end of the long table, acting as his own stand-in. In the last seconds of the four-minute scene, while the camera is on Georgiana, he must get up abruptly, leaving his guests and wife perplexed. History adviser Hannah Greig, lecturer at York University and expert on fashionable society in the 18th century, stands in a corner, careful not to miss a line exchanged between the guests, watching every gesture and movement.

"I sometimes correct the dialogue when it sounds too modern," Greig explains. "Yesterday, one of the characters said 'I'm fine' when he should have said 'I'm well'. As for the male guests in this scene, I have asked them to be more boisterous. I tell them how comfortable they should feel in the presence of the Duke and the Duchess, I give them a sense of the period.

"At the time of the film, there are only 25 dukes in the country, with Devonshire and Westminster the most prominent ones. It's really a small world. The Devonshires are certainly in opposition to the court through their lifestyle. For a member of the aristocracy like Georgiana to have an affair before producing a male heir to her husband was an absolute scandal. As for divorcing, it required an act of Parliament, making it almost impossible. Menage-a-trois were permissible provided they were engineered by men only."

During the 30-minute lunch break, Dibb and cinematographer Gyula Pados discuss the look of the film: "We saw a lot of films from the 1970s like Taxi Driver, The Deer Hunter and The Godfather," says Pados. "Georgiana's life is divided in two - the formal world of the aristocracy and the personal tragedy she's living. We want her to look warm in a cold world."

Filtering the past

Seated next to them, set designer Michael Carlin has had the great challenge of recreating Devonshire House which, standing opposite the Ritz on Piccadilly, was one of the most impressive private buildings in London until the Devonshires demolished it and sold the stones one by one.

"I'm recreating it using different stately homes in Britain, some actually still properties of the Devonshires, like Chatsworth, where we'll be shooting tomorrow," he explains. "Only two facades and the garden have remained intact since the late 1770s - that's what we'll be using. But the search has been difficult, particularly as there are very few Palladian-style houses left in the country. As for the costumes, the colours and the texture, we have been trying to filter the past and have as few ornaments and fussy details as the period allows. My references have been Barry Lyndon and Amadeus."

The Duchess, a co-production between BBC Films, Pathe UK, Kuhn's Qwerty Films and Magnolia Mae films, shot for nine weeks in the UK last autumn. Pathe International is handling sales, with Paramount Vantage snagging US and Australian rights, and Pathe handling distribution in the UK and France. A Venice premiere is the aim.