The Daily Express marked the miracle of Dunkirk with the headline on May 31,1940: “Tens of Thousands Safely Home Already… Many more coming.” British soldiers were still being lifted from the Dunkirk beaches and brought back across the Channel to England as the newspaper went to press. The Express described their rescue as “one of the greatest operations in history”. An accompanying article by trail-blazing reporter Hilde Marchant gave a personal perspective. “It is the greatest and most glorious sight I have ever seen,” she wrote.

Great and glorious was not how most of these soldiers felt as they arrived back in England. Just three weeks after advancing confidently into Belgium to face the German army, they found themselves returning home tired and dispirited, the shambolic remains of a shattered army. Yet this was not how they were received by the British people. They were – for the most part – greeted as heroes. Their return, after all, meant the war was not yet over.

As we approach the anniversary of VE Day, it’s worth remembering just how distant victory seemed in late May 1940. And Britain’s resistance would surely have ended there and then had her Army been mopped up by the seemingly inexorable German war machine. In his speech to Parliament on June 5, made once the evacuation was over and an incredible 348,000 men had been rescued, Winston Churchill called it “a miracle of deliverance” – even whilst cautioning the public that “wars are not won by evacuations”.

True enough, but without this one our modern world would have been very different indeed. And it was a very close run thing. So how did the British Army end up becoming funnelled on to the Dunkirk beaches? What went wrong? And what went right?

Within weeks of the war’s declaration in September 1939, more than 150,000 British soldiers had sailed for France – and there they remained for eight months through the so-called “Phoney War”, waiting for the anticipated German advance. It finally came on May 10, 1940 – the same day Churchill became PM.

The British duly moved into Belgium to meet them but the main German advance was being made further to the south, through the hilly and forested Ardennes region. And it was a spectacular success. Within 10 days of breaking through, German tanks had reached the French coast, all but surrounding the British Army, which was forced into a desperate retreat.

As they turned tail and ran, British soldiers could not at first understand why. But word eventually got around that everyone should make for Dunkirk, the last port not in German hands. From there they could be shipped back to England.But Dunkirk was turning into the least appealing place imaginable. The harbour was put out of action by heavy bombing and the town was on fire, with black oil smoke billowing overhead. Yet the smoke turned out to be a blessing, giving the soldiers something to aim for, as well as protection from the German aircraft prowling overhead.

As troops began pouring into the town, the Germans were kept out by hastily organised British and French units defending the town’s perimeter with orders to fight to the death. A lieutenant given this task, Jimmy Langley of the Coldstream Guards, was approached by an officer of a neighbouring battalion who declared his intention to retreat. Langley and his major gave the officer a stark choice. “You see that big poplar tree on the road? The moment you or any of your men go beyond it, we will shoot you.”

As the officer walked away, Langley and his major fetched rifles. As the man walked beyond the tree, they fired. His battalion stayed where it was. In the meantime soldiers were passing through the perimeter in all manner of states. Some, having retreated through hellish conditions, were bloodied and demoralised. One soldier described his uniform as being so soiled that it had lost its colour, while his socks and feet had merged into a congealed mess of wool and blood.

Vic Viner, a beachmaster responsible for order and discipline at Bray Dunes, recalled experienced NCOs breaking down in tears in front of him. “It’s hard to express how gruesome it was,” he recalled. Elsewhere, a soldier maddened by days without food was spotted trying to eat his leather helmet strap, while several men were seen sitting in a circle on the sand, pretending to eat a meal. Carefully, they mimed the use of knives and forks, all chewing imaginary food.

Yet others have recalled sitting on the beach playing cards as they watched an ex-circus performer accomplishing tricks on the back of a horse. Royal Engineer Fred Carter and his friends wandered away from the beach into town, where they discovered an estaminet – a small cafe serving alcohol. There they spent their remaining money on “a good feed”. Feeling in the holiday mood, Fred decided to try some champagne to see what all the fuss was about. It was, he discovered, “glorious”.

When Royal Navy Sub-Lieutenant John Crosby came ashore at La Panne on May 29 after his ship became stranded on the tide, he made his way to the Hotel Splendide, where he sat with a bottle of wine. For every individual inside the Dunkirk perimeter, clearly, there was a different reality. Stretching for more than 10 miles and populated by hundreds of thousands of men over nearly 10 days of rapidly changing conditions, the whole world was present on these beaches. Tasked with getting these men home – known as Operation Dynamo – was the Royal Navy. In overall command was Admiral Bertram Ramsay, based in the Dynamo Room at Dover Castle, while Capt William Tennant oversaw the evacuation from Dunkirk.

Together yet apart, their job amounted to the improvisation of solutions to unforeseen problems. At first, for example, large naval and civilian ships were sent across to Dunkirk to moor in the harbour and load the men from there, but, with the harbour bombed out of action, the soldiers were sent from the town to the beaches while the ships were sent to moor off the beaches.

This presented a thorny problem: how were the men going to transfer from the beaches to the ships? There were hardly any small boats to ferry them across. At this point William Tennant had a brainwave. The eastern mole – a mile-long breakwater protecting the harbour from waves and silt – could be used as a makeshift jetty.

With a railing at the top and a 15ft tidal drop it was not an ideal pier but something had to be done. So, early in the morning of May 28, Tennant brought a passenger ship – Queen of the Channel – alongside. Men were hurried along the mole and told to clamber on board. Before long, 950 men were on the Queen on their way to Dover. This was improvisational brilliance from a newly appointed leader in a topsy-turvy world. The scenes on the beaches were recreated magnificently in Christopher Nolan’s 2017 film, Dunkirk, for which I was the historical adviser.

The evacuation also featured in the 1964 film Weekend At Dunkirk and, to a lesser extent, in the moving adaptation of Ian McEwan’s 2001 novel Atonement. Today, when people think of the Dunkirk evacuation, the image of the “little ships” tends to come to mind. This was the huge flotilla of boats, collected by the Royal Navy, that arrived after the Ministry of Shipping called for help on May 27. To the men ashore and to pilots flying overhead it was a huge morale boost. More importantly it allowed the beach dwellers to reach the larger ships.

To me it represents a remarkable moment as these tiny boats sailing into a tiny area represented the only exit point from the entire continent. Europe had become a funnel, 3,000 miles wide at the mouth and just 10 miles at the tip. As the Express revealed on May 31, by the mid-point of the evacuation, a narrative was already developing. The undeniable defeat of the British Army was being turned into a triumph. And while it was in the state’s interest to encourage this idea, it was not simply propaganda. Returning soldiers were cheered in the streets, bought drinks in pubs, hugged by strangers. All spontaneous acts.

People were relieved that their husbands, sons, fathers and uncles were safely home and that the war was not lost. They were proud of the soldiers’ last-ditch stand.

And, after all, when had a plucky little army last hurried towards the coast of France, desperate to escape an arrogant and vastly more powerful enemy, only to succeed against the odds and fight its way to freedom? At the Battle of Agincourt, when the happy few had spawned a sense of proud English self. The only sore point was the Royal Air Force, accused unfairly of leaving the beaches undefended by many on the ground. “Where was the RAF?” asked men being bombed and machine-gunned. In fact, Fighter Command flew an astonishing

2,200 sorties during the nine days of the evacuation – losing 87 airmen and more than 100 aircraft to enemy action over Dunkirk, demonstrating the view that the RAF did nothing was absurd. The birth of “Dunkirk Spirit” – the refusal to surrender or despair in times of crisis – was an easy one. It arrived almost fully formed and is still invoked at every opportunity today.

For veteran Robert Halliday, the essence of Dunkirk Spirit was the British and French soldiers fighting fiercely and selflessly on the perimeter to allow the Army to get away. For George Wagner, Dunkirk Spirit was the shared struggle for existence. “We wanted to survive as a country,” he told me. “It was about comradeship and everyone together helping.” When I asked another veteran, Ted Oates, about Dunkirk Spirit, he simply looked at me and shook his head.But Britain had made it through.

• Joshua Levine is author of Dunkirk: The History Behind the Major Motion Picture