Is Brexit the maddest thing England has ever done? Not quite. In its very long history – much longer than most political entities can claim – there is just one episode that is more thoroughly unhinged. It is interesting because it is remembered in England as glorious even though it was morally, politically and economically disastrous. And in this it prefigures the only chapter in English history that comes close to matching its tragic folly – Brexit itself.

At the Tory party conference last October, Jacob Rees-Mogg issued a rallying cry that linked Brexit to the great triumphs of English arms on continental Europe: “We need to be reiterating the benefits of Brexit!” he cried. “Oh, this is so important in the history of our country… It’s Waterloo! It’s Crécy! It’s Agincourt! We win all these things!”

Waterloo might best be left aside, since it was won by an alliance of European armies. But Crécy and Agincourt, two of the great English victories over the French in the 14th century, were indeed remarkable feats of arms – on both occasions the French military aristocracy was virtually wiped out.

The evocation of Crécy and Agincourt as forerunners of Brexit is, however, problematic in two ways. One is that they were English victories but Scottish defeats – the Scots were firmly allied with the French.

The other is that they were part of one of the great criminal follies of European history, the so-called Hundred Years War, the repeated English invasions of France that unleashed on innocent civilians mass murder, mass rape, theft on a staggering scale and an orgy of destruction. It brought nothing but horror and misery. And all in the failed pursuit of a mad idea.

Claiming to be kings

On January 26th, 1340, the English king Edward III stood on a platform in the marketplace of Ghent in Flanders. It was bedecked with new banners commissioned from the workshops of Antwerp, showing the arms of England quartered with those of France. And from that platform Edward declared himself King of France. A Florentine merchant who was there asked some of the locals what they thought. The better sort, he reported, thought the whole thing “puerile”. But for almost half a millennium, until 1802, the English monarchs would go on claiming to be kings of France.

This reminds us of one of the great problems of Brexit: saving face

Edward was not mad. He knew the claim wasn’t real. He made it because he was in dispute with the actual French monarchy about the feudal status of his own vast holdings in the southwest of the country, the duchy of Aquitaine. He needed the support of the Flemings, but they were also feudal subjects of the French monarchy. They couldn’t support him unless he declared that he was in fact king of France. So he did.

This reminds us, though, of one of the great problems of Brexit: saving face. People – and states – don’t act merely out of self-interest. There are times when they make claims they know to be daft. But they can’t find a way to back down.

The claim that the English monarch was king of France started out as a way of dealing with an immediate political problem, just as Brexit has its origins in David Cameron’s strategy for dealing with internal dissent in the Tory party. It, too, was thought of as a kind of deliberate overreach: Edward, like the less extreme of the Brexiters, thought he was making an exaggerated gesture that could be easily bargained away in later negotiations.

But neither Edward nor his successors could find the right means to step down from the platform that he constructed in Ghent in 1340.

Appalling consequences

The consequences were appalling. The invasions of France cost English lives and sucked up English resources. They disrupted and at times destroyed the trade with Flanders and France that had been so important to the English economy.

The insatiable demand for taxation to pay for them very nearly destroyed the English state in the Peasant’s Revolt of 1381. But for the ordinary people of France, the Low Countries, Spain and Italy (all of which were drawn into the conflict) the suffering was immense and seemingly interminable.

The fabulous English military victories at Crécy and Agincourt, at Sluys and Poitiers, did not end the war. As Jonathan Sumption puts it in his magnificent (and still ongoing) multivolume history of the Hundred Years War, they simply “underlined the essential unimportance of battles as a means of achieving anything of long-term significance”.

The English state could not hold conquered territory for long or sustain a large standing army. Its solution was one that would appeal to most of the free market ultras behind Brexit: the war was privatised and outsourced to gangsters.

They stormed towns, raping and killing at will

Sumption (interestingly, now a member of the UK’s supreme court) calls the English strategy “terrorism on a great scale”. Warlords were unleashed on the general population. Edward himself described these men as “outlaws, criminals, murderers, thieves”. The English knight Sir Thomas Gray called them “a horde of yobs”.

They stormed towns, raping and killing at will. They enslaved men and women. They held anyone they thought had money for ransom and tortured them until their families paid up. They stole everything that could be moved and destroyed most of what could not. When they had stripped an area of everything, they moved on to the next set of victims – all in the name of the English “king of France”.

But even the official English armies were savage. The great Italian poet Petrarch, travelling through the area south of Reims a few months after the passage of the English army through it, wrote: “Everywhere was grief, destruction, desolation, uncultivated fields filled with weeds, ruined and abandoned houses…” Shakespeare, in Henry V, dramatises the greatest of the English warrior kings, but slips in an accurate description of the fate of civilians at the hands of his country’s armies.

Henry warns the people of Harfleur what will happen if they do not surrender: “look to see/ The blind and bloody soldier with foul hand/ Defile the locks of your shrill-shrieking daughters;/ Your fathers taken by the silver beards,/ And their most reverend heads dash’d to the walls,/ Your naked infants spitted upon pikes”.

Suffering

This was as all as glorious as the exploits of Joseph Kony in Uganda or Charles Taylor in Sierra Leone in our time. And for what? At the end of all the suffering, English power in France had all but disappeared, the possessions that Edward III had started out with permanently lost to his successors.

The saving grace of Brexit is that it is, so far, a largely bloodless affair. (Jo Cox being its one direct victim.) Even the worst Brexit will be nothing like the catastrophe of the Hundred Years War. But there are perhaps two meaningful parallels. One is the power of the big gesture.

The English claim to the throne of France and the grand rhetoric of Brexit’s revival of the glorious Englishness of Agincourt are bold and thrilling as well as being bonkers – they stir the blood even while they numb the brain. The other is that these grand gestures are far easier to make than to unmake.

It is astonishing how much pain people will suffer and inflict rather than admit they made a mistake. Brexit is not the Hundred Years War, but unless someone finds a way out it now, the consequences will be felt for a century.