When I was growing up, I always assumed that the 99 Flake was so called because it cost 99p. Indeed I think it did for most of my childhood, in what seemed an unusually sensible way for grown-ups to have done things, and perhaps also a nifty reminder of how much to cadge off them to get hold of one.

I doubt there's a single British child that hasn't lapped at the sweet spumy lather of a 99 Flake. It's welded to our youth like chicken pox and bullying. The gentle jingle of Greensleeves from a garishly converted van, a beefy-armed vendor, crisply anaemic cone, turdy curly ice-cream and chocolate spike: it's all a happy reminder of sandy summers and shrieky, milk-smeared faces.



The ice-cream of today's 99s is "soft serve", and ideally around 40% air. A young chemistry graduate named Margaret Roberts was reportedly on the team that developed this profitable way of bulking out a product – her later dealings with milk are notorious. The tiny bubbles make the ice-cream smoother and lighter, and it's served at -4C instead of -15C. I find the cone a papery and insipid thing, prone to sogginess: the 99 cone has nothing on a Cornetto. The hero, of course, is the chocolate.

A 99 is nothing without a Flake. That shattering finger gives depth and body to the scummy, foamy ice-cream and desiccated cone. The Flake emerged around 1920 when a clever worker at Cadbury's Bournville factory noticed that chocolate overflowing its moulds fell and set in appealing ripples. People seem to have spotted its affinity with ice-cream almost immediately. By 1930, Cadbury's was selling half-length Flake "99s" specifically for prodding into Mr Whippy, or his equivalent.

Cadbury's press office sent me some pictures of old Flake packaging which they hoped might accompany this article, adding that we could use the images "providing that there are no negative or derogatory comments made towards Cadbury or its associated brands". Since we aren't using them, this seems an ideal time to remind you about the squalid horror show that was Kraft's takeover of this once great British firm, and also to mention in passing my long-held conviction that Cadbury's cooking chocolate tastes of ashtray and cat poo.

But the 99 Flake is a happier thing. The origin of the name "99" remains opaque, "lost in the mists of time" in Cadbury's inventive phrasing. Numerous explanations have been posited for it over the years. To dismiss two quickly: a Flake is not 99mm long – it predates decimalisation, for one thing – and for most of its history it cost considerably less than 99p. (It's true, though, that Flake 99s did once come in boxes costing 6s 6d, so if you read the box upside down ... ). Some suggestions for the name are brilliantly barmy; there seems little substance to the theory that the name derives from the fact that the initials IC for ice-cream match the pig Roman numerals for 99.

Cadbury's press bumph repeats the fallacious but appealing story that a former king of Italy had a private army of 99 elite soldiers, and that the Italian immigrants who pioneered the 20th century British ice-cream trade used "99" as a corresponding symbol for quality and prestige. The OED briskly deems this tale "without foundation", and the theory was comprehensively exploded by Victoria Coren's BBC show Balderdash & Piffle. I naturally favour the noble tale of Edinburgh ice-cream maker Stephen Arcari, who in 1922 allegedly named the 99 after his shop at 99 Portobello High Street.

Using sex to sell chocolate is hardly new, but the Flake commercials have long been among the bluest in a competitively raunchy market. TV ads for the chocolate have been pulled at least twice, most recently in March this year, while specimens like this from the 1960s are almost NSFW even today. The "Flake girls", of whom around 20 have nibbled and pouted across our screens, were hilariously tacky, reaching a crescendo of naffness around the 1980s with campaigns like this and especially this. They were helped, of course, by the strangulated wail of Ronnie Bond's winningly overwrought jingle, once voted the third most memorable in advertising history.

Cadbury's were meant to have dropped Flake Girl in 2004, the BBC commenting that "her genuine enjoyment … seemed out of step in an age in which knowing irony and parody had become the norm". She hasn't gone altogether, however, appearing recently in an aquatic and impeccably silly Egyptian advert, as well as in this year's hypnotic and very beautiful offering.

One should be wary of using the cliche "iconic" when describing familiar cultural ephemera, and this paper's style guide has stern admonitions against doing so. But that hackneyed adjective nonetheless seems to suit the 99 Flake well. When, a couple of years ago, one company developed a savoury version using mashed potato and sausage, it relied on British consumers understanding the homage and appreciating its irony.

I always thought that two Flakes were de trop in a 99, though I liked an occasional dribble of raspberry syrup, thrillingly called "monkey's blood". Most taxing of all, perhaps, was how to eat the thing. I eventually settled on dipping the Flake in the ice-cream for a few happy bites, then licking the rest in a continuous lateral spiral to avoid dripping, before bathetically munching the sodden cone. How about you?