Rebecca Tyrrel: Illiterate all her life, a Smythson's diary would have meant nothing to Nell Gwyn

Who knew that Samantha Cameron is the direct descendant of Nell Gwyn? She is the great-great-great-great-great-great-great granddaughter of Charles II's mistress.

Although this is going back to the 17th century, it still seems a stronger claim to being less posh than SamCam's insistence, "I grew up near Scunthorpe". While technically correct, what she forgot to add in all the excitement of unveiling her commonness was that the house in question stands in the 300 acres attached to the Sheffield family seat of Normanby Hall ("the jewel of North Lincolnshire").

The beginnings of "pretty, witty Nell", as Samuel Pepys knew her, were a little humbler than that. The daughter of a brothel-keeper, she caught the kingly eye while hired by a former whore, Mary Meggs, to sell fruit at the theatre. She went on in that same theatre to become a star of Restoration comedy. Illiterate all her life, a leather-bound Smythson's diary would have meant nothing to her. Oranges were the only fruit, and David Cameron would approve of that. In 2006, he criticised WH Smith for selling the Terry's chocolate version, rather than the vitamin C-laden one Nell flogged at sixpence a time.

Whether the most lustrous of Sam's ancestors, who include a smattering of Dukes, thanks to Nell providing Charles with two sons, was ever a prostitute herself is disputed. In a 1667 entry recorded in his own diary, Pepys reports her telling a rival mistress: "I was but one man's whore, though I was brought up in a bawdy-house to fill strong waters to the guests; and you are a whore to three or four…". But this may have been as satirical a claim, according to some historians, as Sam's cheeky hint of a Lincolnshire upbringing as grim and joyless as that of Margaret Thatcher.

In an early instance of social mobility of the sort unseen again in royal circles until Kate Middleton became a future Queen, Nell moved into a townhouse a stone's throw from Downing Street in Pall Mall and persuaded the King to give their first-born, Charles Beauclerk, a title. The monarch bequeathed the child the Earl of Burford, a Cotswold town almost exactly the same distance from Sam's current country residence, uncannily enough, as Normanby Hall is from Scunthorpe. It could be that Sam's six-times great grandfather defended himself against accusations of regal pretensions by pointing out that he was in fact dead common, what with being from near Chipping Norton.