My parents, Raymond and Katie, both died young, at least by current standards. Not a day goes by when I don’t miss their presence, but there is also another source of regret. I wish I had pumped them more to talk about the war.

Between 1939 and 1945, both went through a range of experiences that, now, seem awesome. Yet I grew up in a world where everyone’s mum and dad had been through the war.

Dad had been at Dunkirk, Alamein and the Sicily seaborne assault (a bloody rehearsal for D-Day). Mum had lived in London all through the 1940 Blitz and the flying bomb and rocket assault on the city.

These, though, were just normal experiences for that generation. Dad and Mum answered questions about the war if asked, but I never asked nearly enough questions. When they both died in quick succession, there were big gaps in my knowledge.

There are, however, other ways of finding out. After their deaths, I went through the papers stored in their house in Wickford where they had lived since 1948. I came across a postcard. This humble looking, everyday piece of cardboard couldn’t have had more impact if it had gone off like a mortar bomb.

My mother had told me the amazing story behind this postcard, but, until now, I hadn’t realised that it still existed among her possessions.

As a document, it has a significance that stretches beyond our immediate family. The message on that card distills the courage and the high tension at one of the pivotal moments of world history. Here, then, is the story behind that postcard.

Raymond and Katie were married in September 1939, a few days after war was declared. It has become something of a cliché to say that the Second World War was a young person’s war, but by God they were young.

He was a 21-year-old junior hospital doctor who had just gained membership of the Royal College of Surgeons. She was a 23-year-old “Nightingale”, the name given then to nurses at St Thomas’s Hospital in London.

There was just time for a snatched honeymoon in the Kent countryside. Then Dad went off to war. He had gained a commission as a lieutenant in the Royal Army Medical Corps. By the time of the German onslaught, he had been promoted to captain.

That onslaught began on May 10. Within days, German forces smashed the French, British, Belgian and Canadian alliance, driving the allies back to the Channel Ports.

Back home, Brits everywhere knew that the news was grim, although, given the chaos of battle and the lightning speed of the German advance, they had little idea as to exactly what was taking place.

The new prime minister, Winston Churchill, did not mince words. Speaking in the House of Commons, for the whole nation to hear, he spoke of “a colossal military disaster.”

The British forces were now stranded on the Channel beaches. It seemed that the entire army would perish or be captured.

Back in London, my mother was working the night shift. A trickle of wounded servicemen had already arrived in her ward at St Thomas’s.

She was a fluent French speaker, and some of her charges were French soldiers. They tended to be more voluble about events than their tight-lipped British counterparts.

From them my mother acquired an insight into the horror and chaos.

It must have been almost unbearable for her. She had not heard from dad for weeks. Day after day went by, and she increasingly feared the worst.

At the end of a shift, the nurses (all women, back then) would gather to exchange information. “We all had husbands, fathers, brothers, boyfriends in France,” my mother said. “Everything had gone silent. None of us knew where they were. None of us knew what was happening.”

What was happening, of course, was a miracle - the Dunkirk miracle.

A bizarre, impromptu and motley armada of little ships and boats had converged on the Dunkirk beaches, and snatched over 350,000 allied troops from the jaws of disaster. One of them was my dad.

On the morning of May 31 1940, my mother finished her night shift at St Thomas’s and headed for the nurses’ home. On the way, she checked the mail room.

She was used to an empty pigeonhole, but on that morning there was a single postcard addressed to her.

It was dated May 30. My father had written and posted it to her the moment he set foot back on British soil. These are the words my mum read: My Darling Katie, I’ve just arrived in England after a frightful and terrifying journey. But except for a great tiredness I’m perfectly OK & am longing to see you. Directly I can manage to come and see you I will telegram St. Thomas’s and you must be free. I only expect to be here a few days & we will only be able to meet occasionally.

I’ve had to leave every bit of kit I possess & now only possess what I stand up in. C’est la guerre! But anyrate the Boche hasn’t got me.

All my love, Raymond That post-card is now among my most valued possessions, and my own children are under strict instructions to preserve and cherish it down the generations.

If you wanted to explain what was meant by the Dunkirk Spirit, all you have to do is read that message. Dad didn’t actually write the words “Keep calm and carry on”, but he did write the soldier’s version: “C’est la guerre”.

There is also the understatement. The words: “Frightful and terrifying journey” didn’t even begin to tell the tale.

My father, always suspicious of ego-talk, never referred to it. It was left to my mother to tell me some of the things that happened.

On the way home, his ship was dive-bombed. The bombs narrowly missed, but splintered the ship’s rail.

On the Goodwin Sands, an exhausted soldier, sleeping on deck, rolled over. In the absence of a protective rail, he plunged into the sea and disappeared.

My father was a strong swimmer, always impulsive, and bred in the bone to save life. He rushed to the side, ready to dive in after the soldier. Luckily he was held back by some other men. No swimmer, however strong, is likely to survive the seas over the Goodwin Sands.

Dad went on to serve as a field surgeon in North Africa and Italy.

He ended the war as the youngest lieutenant-colonel in the British army in Italy (according to my mum – again, my dad would never have disclosed an achievement like that).

My mum carried on nursing through the London Blitz. In 1944 she achieved her real ambition and qualified as a midwife. There must still be a few wartime babies around, now growing old, who were delivered by her.

She was still in London in 1945 when the bells rang out on VE Day. I asked her how she felt at that moment. “No great joy. Just a big sense of loss,” she said.

Her beloved brother Tommy had been killed in Burma. My father’s brother Martyn, a Hurricane pilot, had been killed in the Battle of Britain.

While others revelled in the streets of London, she stayed at home with her mother. They lit a candle beside photos of Tommy and Martyn, who like so many other young men, had bought VE Day with their lives.

As a family we revisited the Dunkirk beaches, while on a summer holiday camping trip in France.

I remember dad looking around, without much emotion. “It doesn’t inspire many memories,” he said. “There wasn’t much time to take in the scenery. We had to keep our fingers out [a rude phrase, much favoured by my father, meaning not to sit around on your backside].”

One or two random memories did resurface, however. A lot of medical supplies had been lost in the chaos of the retreat.

The field doctors had to come up with all sorts of innovative ways to treat the wounded. It was then that dad came fully to realise the healing and cleansing power of seawater. “Nature’s antiseptic,” he called it.

He also recalled glimpsing a weird spectacle (a lot of accounts of Dunkirk have a surrealist edge).

It was the sight of soldiers trying to burn a vast mound of Woodbine cigarettes, to prevent the fags falling into enemy hands. “Getting a million cigarettes to light at the same time might sound easy, until you see someone trying to do it,” he said.

In some ways (not all) he was a disappointed man. In peacetime he was never able to recapture that sense of driving purpose that must have existed at Alamein or the Gothic Line – or even at Dunkirk.

He blunted his energy and his talent in endless run-ins with the NHS bureaucracy.

I think he regarded post-war Britain as apathetic and self-indulgent.

He found release in his beloved garden. His flower and vegetable beds were kept in military order, like companies of guardsmen formed up for an inspection by the Queen.

Woe betide any enemy blade of grass that tried to infiltrate one of those beds. When he was dying, he delivered his own epitaph: “At least I kept my edges straight.”

Now the Dunkirk Spirit is everywhere again, thanks to Chris Nolan’s magnificent film, Dunkirk.

I had wondered whether the film’s appeal would be confined to British audiences, but it has been a huge hit in the USA as well. Its resonance is universal.

Nowadays, of course, if there was another Dunkirk, there would be many more women on the beaches.

Back in 1940, the likes of my mother could only watch and wait and hope and pray – a young wife, deeply in love, wondering whether those September honeymoon days would become her final memories of my dad.

Thanks to the Little Ships of Dunkirk they were reunited, which is why I am here, to tell their story.

The film once again makes clear just how much we all owe to the wartime generation. Any challenges faced today look piddling compared to the abyss of 1940. Dunkirk has bequeathed us a reservoir of inspiration. The time may come when we badly need to draw on it again. In the meantime, as I look at that postcard, all I can do is make a pledge to my mum and dad, Raymond and Katie. I will keep my edges straight.