In a country as famed for its idiosyncrasy as England, the Fourth of June still stands out. Eton College’s open day is named for the birthday of George III but never falls on the eponymous date. History kindly overlooks whether a guest has ever arrived on the actual 4th of June or detected irony in the question: ‘When is the Fourth of June this year?’

Having assimilated this overarching bloody-mindedness, the visitor enters an environment replete with the quiet semiotics of an old institution. The famous uniform of stiff-collar-and-tails now has as many adornments as that of a minor military junta. A grey waistcoat with silver buttons means something very different from a coloured waistcoat. And so on. And on, and on. The Gormenghast-like vocabulary of the place is not even to be attempted.

To the boys, The Fourth of June means something very specific: girls. It is hard to describe the fervour that grips a male boarding-school house on waking to the prospect of an influx of maidenhood. Last-minute press-ups are performed and bottles of cologne emptied onto unshaven cheeks. Sisters are key intermediaries, distributing the coveted invitation among their clans. In the summer term of a girls’ school, even the bluest of blue stockings becomes the toast of their school year: if they have a brother at Eton. Once on the field of battle, only the bravest of either sex truly engage the enemy. Oiling the wheels of success and failure, the business of clandestine drinking is taken very seriously.

Or was. The organising principle of the day has changed from fecund chaos to a technocratic insistence that things pass off uneventfully. Family picnics – which once provided the central matrix for drinking and flirting – have been briskly consolidated into catered events by individual Houses. Parents were once lords of their own rug, entertaining whom and how they chose. Now they mill about awkwardly under a shared marquees like unwilling neighbours at a local cook-off. Where teenagers were once elevated to the level of adults, now adults are infantilised into the parameters of a school House. Housemasters are slippery as to whether this iniquity had evolved naturally or been imposed from above. Either way, a day that was once about giving back to the fee-payers is now ever-more about The Boys. They reciprocate with a recrudescence of teen indifference, slumping in unbuttoned waistcoats while their guests tire in the sun.

The day’s denouement is the Procession of Boats. The answer to why several dozen half-sober teenagers should have to stand up in a moving Eight, lift their oars vertically, then shake loose from their boating hats garlands of flowers is, of course: why not? The spectacle used to be greeted by a self-organising mass of half-drunk spectators, all baying eagerly for calamity. Now the guests’ glasses are taken from them on the way to the riverbank. A seated – and ticketed – enclosure has been erected, and the dead hand of Live Commentary been introduced. The brass band survives but is no longer centre stage. Without the moral support provided by the Boating Song and Happy Birthday – for George III, course – ever more of the crews seem to fall in.

But there is another way of looking at this: the change has been wrought not within the school but simply by growing up. Perhaps the 1200 souls of the five Blocks will enjoy this year’s Fourth of June as keenly as we did in the Nineties? Yet it’s hard to avoid the thought that Eton has diluted its exceptionalism to survive; or the hope that in some post-apocalyptic future, the family picnic will return.

The Fourth of June is this Saturday – the 16th of June.