The version of the Christmas truce of 1914 that has taken root in popular culture seem extremely far-fetched. In Michael Foreman’s children’s novel, War Game, the conflict is broken up so that soldiers may play a disorganised game of football, “their faces wreathed in smiles and clouds of breath in the clear frosty air”. In the 2005 film Joyeux Noel, soldiers carry Christmas trees into no-man’s-land, and listen together as an opera singer serenades them. And in Oh, What A Lovely War!, British troops dive for cover when a missile is thrown from the German trenches – only to find that it’s a boot filled with sausages and chocolate. These tales are almost unbelievable.

But they are entirely true to life. The mythical quality now carried by that extraordinary interlude is not the result of creative licence or revisionist sentimentality: it is rooted in the facts. The man who seems to have been the last surviving witness to those strange days, a Scottish infantryman called Alfred Anderson, died in 2005 at the age of 109. But the many contemporary accounts that survive tell an improbable and bottomlessly moving story. If the version we remember today falls short in any respect, it is this: it doesn’t go far enough.

The Christmas truce was not organised. But it was predictable, and it was predicted. A few weeks earlier, the commander of the British 2nd Corps, General Sir Horace Smith-Dorrien, issued a warning to his senior officers. “It is during this period that the greatest danger to the morale of troops exists,” he wrote, warning that soldiers might slip into a “‘live and let live’ theory of life”. Divisionary commanders were told that “friendly intercourse with the enemy” and “unofficial armistices, however tempting and amusing they may be, are absolutely prohibited” lest they “destroy the offensive spirit in all ranks”.

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But it was no use. By the time Smith-Dorrien sent his memo, pockets of goodwill were already breaking out. The war was only months old, but with more than a million already dead, the gung-ho spirit that animated the first volunteers had already been sapped away. The front lines were barely moving; in places, they were no more than 60 yards apart, making it easy for shouts to carry back and forth. If these were mostly insults, they were, according to Rifleman Lesley Walkinton of the Queen’s Westminsters – quoted in Stanley Weintraub’s Silent Night, an engrossing short history from which a number of other accounts in this piece are taken – mostly expressed “with less venom than a couple of London cabbies after a mild collision”. Elsewhere, the guns would go quiet during the breakfast hour, allowing men to get water and rations before getting on with the business of trying to kill each other. And on the morning of 19December, an impromptu ceasefire on one stretch of the line allowed men from both sides to come out and bury their dead.

Still, it was the spur of Christmas that made these oddities into a phenomenon. Malcolm Brown, a historian at the Imperial War Museum and co-author of another book on the subject, Christmas Truce, has estimated that a short peace broke out along about two-thirds of the British line. In most accounts, the initiative comes from the German side, perhaps because they were in the ascendant, and so felt more secure. On 23 December 1914, for example, halfway between Ypres and Lille, soldiers from Leipzig started putting small fir trees – tannenbaum – on the parapet of their trenches, with candles clamped on to provide a seasonal glow. With no guns firing, their British counterparts crawled from their trenches to gaze at the display. They looked, one said, “like the footlights of a theatre”.

Not everyone understood, or subscribed, to the gestures of goodwill being made along the line. On Christmas Eve, Muslim soldiers from Algeria on the British side, unaware of the peculiar rules that were taking hold, fired upon the German forces across from them. According to a story related by the German children’s writer James Krüss, and apparently told to him by his uncle Otto, a pastry chef from Berlin called Alfred Kornitzke was particularly enraged by this breach of decorum.

Kornitzke, or so the story goes, had been in the process of making marzipan balls for his company when he had to take cover; his blood up, his baker’s hat still on, he grabbed a tannenbaum and strode out into no-man’s-land. With the Algerians too bemused to shoot, he set the tree down and lit the candles. “Now, you blockheads,” he is said to have shouted, “now you know what’s going on! Merry Christmas!”

As night fell on Christmas Eve, bringing with it a hard frost, the soldiers who had traded insults up and down the line instead began to sing for each other. In his reminiscences of the war, Rifleman Graham Williams of the Fifth London Rifle Brigade described how the spirit took hold: “suddenly lights began to appear along the German parapet,” he wrote, “makeshift Christmas trees, adorned with lighted candles, which burnt steadily in the still, frosty air! … First the Germans would sing one of their carols and then we would sing one of ours, until when we started up “O Come, All Ye Faithful” the Germans immediately joined in singing the same hymn to the Latin words, Adeste fideles. And I thought, well, this is really a most extraordinary thing – two nations both singing the same carol in the middle of a war.” Many of the men stayed awake all night.

Not all of the music was amateur. In one section of the front, where Germans faced French soldiers, a famous operatic tenor, Walter Kirchoff, was visiting in the company of Crown Prince Wilhelm. (By and large, there were fewer truces with French troops, who were less easily persuaded of the case, fighting as they were on their own soil.) While the heir to the throne stayed back, Kirchoff made his way to the very front line. Years later, French, German and English soldiers alike all remembered hearing him. As he sang, he later said, enemy soldiers applauded from the parapet, and called for an encore.

The truce proper began in as many different ways, at as many different times, as there were groups of soldiers to enact it. In some places, Germans held up signs bearing a phrase in broken English: “You no shoot, we no shoot.” In others, it took remarkable faith in the forbearance of the other side. According to the memoir of Private W J Quinton of the 2nd Bedfordshires, on his stretch of the line, the peace began in the dark, with another call for an encore after a song from the enemy. At that, a German voice called out from no-man’s-land: “I am a lieutenant! Gentlemen, my life is in your hands, for I am out of my trench and walking towards you. Will one of your officers come out and meet me half-way?” The suspicion of an ambush at first stopped the British men from doing so, and, with dozens of guns pointed in his direction, the German appealed again. Again, there was no response.

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“Gentlemen!” he cried. “I am waiting!”

Finally, an officer from the Bedfordshires summoned his nerve and headed out into the darkness. The singing from the Germans grew louder. And the two men negotiated the terms.

The accounts of Christmas Day itself that later appeared in letters to newspapers and loved ones have an other-worldly, incredible quality to them; they read like the memories of events that already felt unreal as they happened.

“We shook hands, wished each other a Merry Xmas, and were soon conversing as if we had known each other for years,” wrote Corporal John Ferguson, of the Second Seaforth Highlanders. “We were in front of their wire entanglements and surrounded by Germans – Fritz and I in the centre talking, and Fritz occasionally translating to his friends what I was saying. We stood inside the circle like street corner orators …. What a sight – little groups of Germans and British extending almost the length of our front!”

Mementoes, such as buttons, belt buckles and the famous German spiked pickelhaube helmets, were exchanged, along with more immediately useful gifts: tobacco, food, and alcohol. In one spot, an initially tense encounter burst into exuberant, careless life when a hare darted out from an abandoned cabbage patch, prompting a chase in which German and kilted Scottish soldiers competed for the quarry. “The game was won by the German who captured the prize,” one participant wrote. “But more was secured than a hare – a sudden friendship has been struck up, the truce of God has been called, and for the rest of Christmas Day not a shot was fired along our section.”

Often, communication difficulties were eased by Germans who had spent time in Britain – a feature of the day that must have made the enforced state of enmity seem stranger than any other. “Watcha cock,” a German soldier said to Graham Williams of the London Rifles, “How’s London?” The man turned out to be a “German Londoner” who had grown up in England but had been recalled for national service from his porter’s job at Victoria station.

A Londoner in the 3rd Rifles was reported to have had his hair cut in no-man’s-land by the man who had been in his barber in High Holborn. As he shaved his old acquaintance with a cut-throat razor, he underlined the peculiarity of the circumstances with a joke: “Maybe I should cut your throat, yes? Save ammunition tomorrow.”

Another had a wife and five children near Birmingham; still another asked Lieutenant Sir Edward Hulse to send on a postcard to the “best girl” he had left behind in Suffolk along with a 3½ horsepower motorbike. Hulse agreed to do so, warning the German (he later wrote to his mother) “that she probably would not be a bit keen to see him again”.

The peace that reigned rendered the battlefield suddenly alien from the miserable new home that had become so familiar. “From all sides birds seemed to arrive, and we hardly ever see a bird generally,” Hulse wrote in the same letter. “Later in the day I fed about 50 sparrows outside my dug-out, which shows how complete the silence and quiet was.”

Nor was the sense of an alternative reality confined to the land forces. On Christmas Eve, the Royal Flying Corps dropped a carefully-packaged plum pudding on an enemy airfield at Lille; on Christmas Day, their German counterparts responded with a bottle of rum.

And then there was the football. While there was no organised 11-a-side match between British and German forces, there were, indeed, chaotic kick-abouts up and down the line, usually with dozens of participants and no obvious rules. A ball was variously improvised from a ration tin, a sandbag, or a woolly hat stuffed with straw. Rowan Atkinson’s Edmund Blackadder was later to protest – “Remember it? How could I forget it? I was never offside! I could not believe that decision!” Sadly, this does not appear to have any basis in fact.

The truce was not observed perfectly. Accidental gunfire occasionally led to panic, and in one particularly grim incident, Sergeant Blackwood Jones recalled a comrade who took some tobacco and jam to the Germans, only to be shot in the back as he returned to his trench. “He fell down and said, ‘My God, I’m done’,” Jones wrote. “They are dirty cowards, after [our] giving them tobacco.” On the British side, too, there were those whose hatred for the enemy would not allow them to observe any kind of peace.

In time, of course, it had to end. It did so as it had begun: gradually, variously, apparently in a state of surreal isolation from the normal rules of war. At first, soldiers reluctantly followed their enraged superiors’ commands to fight by firing into the air. Sometimes a few frenzied individuals would spark a section into battle again. And, eventually, units that had established such an extraordinary bond were rotated away from the front, to be replaced by others with no such fine feeling for their opponents.

If the Christmas truce carries an almost unbearable poignancy, the postscript is perhaps the saddest aspect of all. There were no more such truces: while a few isolated moments of peace descended in later years, the Great War would never again see the phenomenon on such a widespread basis. The reasons are simple, and grim: the war got worse. The tactics became barbaric. The man across the field from you ceased to be a barber from High Holborn, and became an inhuman force. “As the war goes on, the enemy becomes increasingly abstract,” Modris Eksteins, a cultural historian who has written on the subject, told The Washington Post. “You don’t exchange courtesies with an abstraction.”

Today, now that the last participants have gone, the Christmas truce seems more than ever to straddle two alien ages: a time when conflict was chivalrous, and bloodshed might be prefaced by a gentlemanly handshake; and a time when the cavalry officer was replaced by the tank commander. It seems a relic of a bygone age in other ways as well. Britain’s most recent wars, after all, have not been fought with Christians, or conducted in static trenches, where the enemy are a mere carol away. And yet it still feels resonant; still seems to speak of the possibility of human warmth even in the grimmest circumstances. The strange contradiction it embodied is summarised best of all, perhaps, by a doggerel poem written by a member of the British 63rd division:

I do not wish to hurt you

But (Bang!) I feel I must.

It is a Christian virtue

To lay you in the dust.

You – (Zip! That bullet got you)

You’re really better dead.

I’m sorry that I shot you –

Pray, let me hold your head.

In tomorrow’s Independent : The battle of Dogger Bank.

The series can be seen at independent.co.uk/greatwar