What is the easiest way of changing one’s outdoor appearance? Buy a hat. I did it as an undergraduate in Cambridge (it was a homburg, and caused me to be described in the pages of the Spectator as “a pale imitation of Enoch Powell”) and I have just done it again. And where does one go to buy a hat? To Lock’s, of course.

The firm of James Lock & Company was founded in 1676 and therefore can claim to have acquired a decent measure of experience in the provision of headgear. It now resides at number six St James’s Street, handily close to a number of London’s more civilized destinations. So a pleasant morning can be had, buying a couple of paintings at a Christie’s auction, being measured for some shirts in Jermyn street, selecting a hat at Lock’s and then toddling off to the Ritz for lunch.

Still owned and run by descendants of Mr Lock and of his business partner, the shop is narrow, long and has a properly old-fashioned atmosphere. In the corner is a handsome long case clock. Do not overlook it, for it is an important timepiece – important enough, indeed, to be the subject of an article in Antiquarian Horology. Its top dial allows you to calculate the time of sunrise and sunset on any day of the year – although it is always 10 days early, having been made before the introduction of the Gregorian calendar in England in 1752. Looking closely, I spied the words ‘No real night’. What on earth did they mean? Well, it seems that there is a period between May and July in England during which the sun does not sink low enough below the horizon to be classified, astronomically, as night. Remarkable.

As is the list of Lock’s customers. The warrants of the Duke of Edinburgh and his son hang on the walls. Of other current customers the firm is discreet, but past notables such as Lord Nelson, Charlie Chaplin, General de Gaulle, Oscar Wilde, Beau Brummel, Laurence Olivier and the Duke of Wellington all covered their heads the Lock’s way. (One of the Iron Duke’s swan-feathered hats can still be seen in the shop, an impressive tribute to the longevity of the firm’s products.) And customers occasionally contribute more than their distinction. Sometimes hats are named after those for whom they were first made. Thus the Coke. The Coke? Yes, long before the American fizzy drink, Mr William Coke asked Lock’s to make a hard, rounded hat for his gamekeepers. Thus was born what people outside the world of Lock’s know as the bowler hat – made of muslin, stiffened with shellac.