“The dresses are an absolute nightmare because you can’t breathe” revealed Keira Knightley, of her authentic 18th century costume. “But it kind of helps because if you’re feeling at all emotional then it makes it ten times worse as you can’t catch your breath, so that helps in playing the scene.” Miss Knightley continued: “The worst part is after lunch, because they’re so tight they don’t help digestion which meant that Hayley [Atwell, co-star] and I were there playing these very ladylike characters but belching all over the place!”

Like Princess Diana, her direct descendent, Keira’s character Georgiana Spencer, Duchess of Devonshire is beautiful, glamorous and adored by the public.

It seems the fact that filmmakers use an image of Diana in the trailer and the words “history repeats itself” hasn’t gone down too well: “I didn’t think it was going to be made such a big deal of - perhaps stupidly” said Keira. “I really don’t know the Diana story well enough to know what the similarities are but I think Georgiana’s a fascinating character in her own right. It’s an interesting bit of trivia that they were distantly related, but for me it didn’t go any further than that.”

After finding herself stuck in a loveless marriage, Keira’s Duchess falls in love with with Charles Grey, later the Prime Minister, played by another young British actor Dominic Cooper (Mamma Mia, History Boys). We asked Keira about shooting those steamy love scenes….

“I couldn’t stop laughing. He’s a very good looking guy but he’s standing there naked apart from a skin coloured nappy. It’s the most unsexy thing ever. The director even had to ask if I could be a little more supportive and I had to say no - he’s wearing a nappy!”

The Duchess is in cinemas across the UK on September 9th.