That might seem to be a counsel of despair, until one remembers that a significant minority recently identified Churchill as being the name of a talking dog in an insurance commercial. Historical dramas such as The Duchess are hugely important. Having myself been enormously inspired by the rash of ruff and hosiery movies I saw as a child at my local suburban Odeon, I don’t underestimate the part that popular culture can play in conveying something deeper, and ensuring that it stays in the public ­imagination.

So one should sometimes overlook liberties taken in the service of something higher. In 1972, for example, Hal Wallis’s Mary, Queen of Scots had Elizabeth (Glenda Jackson) and Mary (Vanessa Redgrave) meeting in secret (and not just once, but twice, which really seems to be pushing your luck). When I got round to Antonia Fraser’s biography, I discovered that of course such incidents never took place. But the point is that it was the film which brought me to the book in the first place.

The Duchess concentrates on Georgiana’s marriage to the stone-cold Duke (played here with his trademark petulance by Ralph Fiennes), the much talked-about domestic arrangement she tolerated with his mistress, her best friend Bess Foster (portrayed by the superb newcomer Hayley Atwell) and her subsequent affair with Earl Grey. The latter’s Whiggish wig is filled by Dominic Cooper, whom you might last have seen as the beach hunk in Mamma Mia (or maybe not).

Having been primed beforehand, parallels with Charles, Diana and Camilla keep popping into one’s head, helped along by much of the dialogue. “He must be the only man in England,” someone says of the Duke, “who’s not in love with his wife.”