I have never lost my admiration for Boris Johnson’s summary of British ambitions over Brexit as ‘having our cake and eating it’. It taught a generation of EU bureaucrats an important English idiom.

So it is with renewed admiration, if involuntary distaste, that I regard his success in reintroducing turd into polite conversation. It has been used openly on Radio 4 at breakfast-time, ever since Mr Johnson was reported to have remarked during the Chequers cabinet meeting (or kidnapping) that defending the Brexit plan would be like ‘polishing a turd’. The Oxford English Dictionary gives the proverb ‘You can’t polish a turd’, comparing it to ‘You can’t make a silk purse out of a sow’s ear’. Turd polishing is found no earlier than 1976 and is not to be confused with turd packing, a homophobic term. But I am sorry to report that turds have played a large part in proverbial lore for centuries, always fairly disgustingly.

Turd itself, the dictionary notes, is ‘not now in polite use’, although that might have changed last week. In the Middle Ages it was an ordinary word for a piece of excrement, being used in 14th-century Bibles – as in the prophet Zephaniah (1:17), where the Authorised Version has dung. St Paul was even made to say: ‘Alle thingis I deme as toordis, that I wynne Crist.’

For ‘animal droppings’ it continued to the present day in dialectal forms, as treddles, truddles, triddles or turdles.

Turd became coarse because of its success in abusive phrases, such as the revolting turd in your teeth, as Ben Jonson bears witness. Its power spawned 20th-century insults like turd in the punchbowl or as popular as a turd in the fruit salad.

From the 1960s, in Private Eye, turd was taken up enthusiastically in the name for the popular band Spiggy Topes and the Turds. As a fairly recondite scatological term, it took turns with ordure, as when Peter Cook, in his fantasy summing up by the judge in the Jeremy Thorpe trial, referred to the failed hit man: ‘He is a piece of ordure, a piece of excrement, unable to carry out a simple murder plot.’ It was certainly not applied to polished performances.