At the end of May, 1940, 338,000 British and French soldiers were evacuated from Dunkirk at the end of a campaign that had seen Hitler’s forces more or less surround the Allied armies: their only line of escape was over the sea.

They were rescued by the Royal Navy and those famous little ships, aided by the soldiers who held a string of strongpoints around the corridor up which the bulk of the Army was retreating. Most of the men who made those last-ditch stands were killed, wounded or captured.

Only a few managed to join the great exodus. Their journey to the sea is portrayed in the screen adaptation of Ian McEwan’s novel Atonement. James McAvoy plays Robbie Turner, one of those soldiers: but were his experiences anything like those known to the real soldiers?

In May, 1940, Julian Fane was a 19-year-old 2nd Lieutenant in the Gloucestershire Regiment. After playing his part in the defence of the strongpoint of Cassel, he was ordered to creep out of the town on the night of May 29 with the remnants of his battalion. By then, Cassel was surrounded by Germans and the 20-mile trek to the coast meant passing through their lines. Few of those in the withdrawing column made it. They had not travelled five miles from Cassel before they were ambushed. Many were killed or captured, but Fane and some others slipped through – just as Robbie Turner and his men do in the film – reaching Dunkirk hours before the evacuation ended.

Although Fane is now an 86-year-old grandfather (he ended his military career as a lieutenant-colonel), he vividly remembers the ambush, and being trapped in a wood. “We must have been spotted by the Hun,” Fane told me, “for we had not been there long before the whole area around the wood resounded with the cries of ‘ Kamerad!’ There were a lot of troops shouting this treacherous word. Then they all stopped, and a voice started speaking in clear tones in very good English: ‘Come out! Come out! Hitler is winning the war. You are beaten. Come out, or we shall shell you out. Lay down your arms and come out running.’ It was a nasty moment, for we all realised the hopeless position we were in. One false move and we would all be shelled to hell.”

Some of the soldiers in the wood were killed and many captured. However, by remaining quiet and frequently shifting their position, the soldiers accompanying Fane avoided the shells and shrapnel that rained down. At nightfall they slipped away unobserved, only to be ambushed in an open field. “Everyone threw themselves to the ground. Lieutenant Dick Olive, in front of me, caught a blast of machinegun fire in the chest. His lungs began to fill, and I shall never forget the rasping noise of his breathing. It took about two minutes before he drowned in his own blood. Company Quartermaster Sergeant Farmer, also next to me, got a burst of tracer in the back which set off the rounds he was carrying in a bandolier over his shoulder. The tracers lit up the country like a firework display.”

After scrambling away down a ditch, Fane and some 11 men eluded their ambushers. But, like Robbie Turner in the film, Fane had been wounded – hit in his right arm during the second ambush. If his journey had lasted much longer, he might have succumbed to the septicaemia that so strikes Robbie. Fortunately the soldiers under his command helped him to survive, for example (just as in the film), by letting him sleep longer.

They marched on in spite of blisters, trench foot (a severe form of athlete’s foot brought on by crossing numerous streams) and lack of food: their only sustenance was what they found in abandoned houses. Their ordeal was prolonged because Fane decreed that they must hide in ditches or farm buildings during daylight and march only at night.

Mirroring the action in the film, they received their nastiest shock when Germans entered a barn where they were resting: they were undetected because they were hidden by bales of hay. “We were paralysed with fear and I began to sweat profusely,” Fane remembers. “Imagine my horror when I saw a face appear over the top of our straw barricade. It was a civilian, luckily. He said one word, ‘ Schlafen [Sleep],’ and then disappeared after Corporal Eldridge beckoned him to keep quiet and go away.” Miraculously, the Germans never heard Fane’s men fidgeting and sneezing, and they eventually departed.

During the third night they met a column of horse-drawn artillery. “We thought it must be French,” Fane recalls. “Leaving my party hidden, I went up to a man riding a bicycle and addressed him in French. He replied: ‘ Ich verstehe kein Französisch,’ and fortunately moved on, while I melted into the night with as much dignity as I could assume, fearing that at any minute I might get a bullet in my back.”

Fane and his men had many more close shaves during the next night: Corporal Eldridge gripped Fane by his shoulder and whispered: “My God, sir. Look out!” Fane saw a German sleeping on the ground at their feet. They stepped around him, and left him to his slumbers. Then, on a country lane, they dived into the hedges as German tanks nearly crushed their legs as they roared past. One road was so full of German traffic that they crouched by the roadside for what seemed like hours. “One man made regular trips up and down on a two-stroke. How we cursed him. At last, at dawn on June 2, after four nights, they reached the beaches east of Dunkirk which, as depicted in the film, were covered with British soldiers.

Fane was one of only 57 Gloucestershire Regiment soldiers who made it back to England. That was the last he saw of the men he had led, although he later discovered that some of them had got home.

“When I was at Sandhurst before the war we learnt that we might have to fight to the last man. But I never dreamt it would come to that. We survived so many near-misses, and only got home because we were very lucky.”

Dunkirk: Fight to the Last Man, by Hugh Sebag-Montefiore, is published by Penguin, £7.99.

— The film of Atonement is released on September 7

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