The past was always conjured in Brexiters’ dreams of the future, as it was in Donald Trump’s stump speeches across the Atlantic. The winning power of the Brexit campaign slogan used by the U.K. Independence Party leader Nigel Farage, “We want our country back,” lay partly in its vagueness, which let it appeal to all manner of disaffected constituencies, but also in its double meaning. “Take it back” in the sense of saving the nation from things perceived to threaten it — seen variously as immigrants, faceless European Union bureaucrats, globalization, the “Westminster elite” of Britain’s political establishment — and “take it back” also in the sense of back in time, to some ill-defined golden age. Preserving a continuous national heritage and tradition was an explicit part of the “Leave” campaign. For years I had read in tabloid articles that the E.U. was destroying much-loved English traditions — baseless claims that its bureaucrats were going to ban everything from English breakfasts for truck drivers to the queen’s favorite dog breed, even barristers’ wigs. The quaintness of these conjured shibboleths was no accident: Brexit rhetoric was all about a battle to save English values and an English way of life beleaguered by waves of immigration and European interference. It had weaponized history and tradition.

In its antiquity, its pageantry and its evocation of deep English history, the subject of Spencer’s painting exemplified these themes, and I wondered if seeing swan upping firsthand could help me understand a little more about the state I was in. In a few weeks, the uppers would set out on their journey. I decided to go with them for part of the way. I could have chosen to witness any number of English customs, from Morris dancing to village cricket matches, but swan upping drew me, partly because of the painting but also because I’m fascinated by the relationship between natural history and national history. Symbolically, swans have long been entwined with nationhood and identity. Politics is bound up with them.

The swans on the Thames are mute swans, a native species with a curious history in Britain. In past centuries, when they were commonly served roasted at feasts, fewer free-flying wild ones existed here, and even today they seem to me more like feathered livestock than birds: huge, faintly menacing inhabitants of local parks and rivers, neither fully wild nor fully tame. Swans’ royal ownership dates at least to the 12th century, and certain flocks — known traditionally as games of swans — were granted by royal charter to hundreds of favored dignitaries and institutions. All the young swans in the country were once upped each summer, the last joint of one wing cut away to render them flightless, and patterns incised in their bills or webbed feet to establish ownership. Exquisitely inked manuscript records of these marks still exist: lines and crosses scribed across diagrammatic beaks. As geese and turkeys became popular eating — less territorial than swans, they were much easier to keep — ownership of swan flocks reverted to the crown in all but a few locations, like the Thames.

In Britain, killing a swan still generates unexamined outrage: It is wounding the body politic, a thing akin to treason. The symbolism of swans is so commonly understood in Britain — emblems of the monarchy, and by extension the nation — that these birds have long been counters in the game of what is us and what is not. Perceived threats to swans closely track the imagined enemies of British society. All the swans on the Thames, or so one story goes, were killed by Cromwell’s soldiers during the Civil War, and the river was restocked only with the restoration of the monarchy. Mournful 19th-century obituaries for Old Jack, the swan who lived at the seat of the monarch at Old Buckingham House, relate how his decades-long reign over his pond was brought to an untimely end by a gang of warlike Polish geese. A 19th-century magazine article claimed that swans in the royal parks were killed and skinned and their remains tied to trees by Jewish feather traders.

It’s easy to read these fables of nationhood as curios from another age. But they are not. In the early 2000s, the Sun tabloid accused asylum seekers of stealing the queen’s birds for barbecues. Later it transpired that the basis of the story was a telephone call to a swan sanctuary to report that someone had been seen pushing a swan in a shopping cart.