The like, it was said of the Thames Pageant, had not been seen for 350 years and would not be seen again. Something similar might well be said of almost every ceremonial event during the holiday weekend, even of the Palace pop concert, which brought together so many old faces as well as (comparatively) new. Indeed, it could be said of the Diamond Jubilee itself. But it was most true of yesterday's thanksgiving service at St Paul's Cathedral, the occasion where – it was widely noted – the Queen looked most comfortable and at home.

Here, truly, was a Britain, whose like will not be seen again, because it is passing so swiftly into history. It was not just the carriage procession from Westminster Hall, or the cavalry, or the massed military bands, with their air of empire and antiquity, that harked back to another age – they have a few outings left in them – but the church service itself, and above all the congregation: mostly white, of a certain age and a certain background. But the Anglican cathedral experience is no longer as widely shared as it was. As the flag-waving crowds on the Mall testified, Britain is already a different place.

In this respect, the Queen's Diamond Jubilee may with hindsight be seen not only for the extravagant spectacle and popular festival that it was, for the pageants and the street parties, but as the last hurrah for a way of doing things that is now, for most of the population, in the past. From the balcony of Buckingham Palace yesterday the visual message was one of stability and continuity, but also of a monarchy pared to its essentials. Only the Queen, her son and heir, and his two sons, and spouses, came out to greet the crowds. There was a solemnity of purpose here.

In her six decades on the throne, Queen Elizabeth II has trodden an often delicate line between observing tradition and modernising. At times, the institution lagged behind the people; with last year's marriage of Prince William to Catherine Middleton, the two came back into sync. But as this celebration fades into memory, so it may start to look more and more like a valediction: a glittering – if endearingly rain-sodden – coda to a departing age.