A member of the German S. S. Einsatz Gruppen D prepares to shoot a Polish Jew who is kneeling on the edge of a mass grave almost filled with previous victims

The scene is a German town called Gleiwitz close to the Polish border. Here, on the night of August 31, 1939, a small group of Nazi intelligence agents, dressed in Polish uniforms, burst into a German radio station.

There they broadcast anti-German messages in Polish before dumping the bodies of prisoners they had just hauled out of the Dachau concentration camp, who had been made up to resemble Polish saboteurs then shot and mutilated to make identification impossible.

A few hours later, Adolf Hitler rose in the Reichstag and announced that the Gleiwitz incident — which he, entirely deceitfully, blamed on anti-German saboteurs — was the final straw.

Already, Nazi forces were flooding across the border into Poland. The darkest chapter in human history had begun.

In Britain, we remember World War II as a story of unparalleled heroism, the stuff of stirring films such as the new blockbuster Dunkirk. For the people of Poland, however, the war was a nightmare so black, so bloodstained, that no film could even remotely capture the depths of its horror.

By the summer of 1945, some six million Polish citizens, one in five of the pre-war population, had been killed. The great cities of Warsaw, Krakow and Lublin were in smoking ruins. Millions of books had been burned; hundreds of libraries, schools, museums and laboratories had been destroyed.

In effect, the Germans had done their best to eradicate an entire nation, erasing its culture, murdering its middle-classes and reducing the rest to slavery. And though the Nazis were defeated, the Polish people’s ordeal was far from over, for the end of Hitler’s tyranny saw their country occupied by Stalin’s Red Army, who turned it into a brutalised Soviet satellite.

Cremation ovens in Majdanek concentration camp (officially known as KL or KZ Lublin) in Poland, 1944/1945 after the liberation by the Red Army in July 1944

It is no wonder, then, that many Poles have never forgiven what happened on August 31, 1939. And perhaps it is no wonder, either, that the leader of Poland’s ruling conservative party, Jaroslaw Kaczynski, is now demanding ‘huge sums’ in reparations from the German government.

There is, of course, a political dimension to all this. Mr Kaczynski is an uncompromising and unapologetic nationalist who is currently embroiled in a fierce row about his attempts to tame Poland’s independent judiciary. So a sceptic might be forgiven for suspecting that, coming in the week when Poles are remembering the doomed Warsaw Uprising against Nazi rule in 1944, Mr Kaczynski’s outburst was more of an attempt to secure his nationalist base than a serious effort to right the wrongs of World War II.

On top of that, the legal situation is very murky. Poland actually waived its right to reparations from the Germans at the end of 1953, though Mr Kaczynski and his allies have always argued — not unreasonably, I have to say — that this should not be binding because it came as a result of pressure from their Soviet occupiers.

As a rule, I am usually very sceptical about the idea of reparations for historical crimes. Some activists even claim that Britain should compensate African and Caribbean countries for its involvement in the slave trade — an argument I find totally unpersuasive.

Jewish residents in Warsaw are working as forced laborers in the streets of the Polish capital. (Undated picture)

But if any country deserves restitution after its suffering in the last century, then it is surely Poland. Indeed, few of us in Britain can even begin to imagine the awfulness of the ordeal the Poles endured after the first German tanks crashed across the border.

Hitler’s intentions were chillingly clear from the very beginning. Poland was to be cleansed of its existing population, whom he regarded as sub-human, in order to make room for German colonists.

Ten days before the invasion began, he told his commanders that they should kill ‘without pity or mercy, all men, women and children of Polish descent or language’. And in March 1940, the SS chief, Heinrich Himmler, was even more explicit. Soon, he said, ‘all Poles will disappear from this world. It is imperative that the great German nation considers the elimination of all Polish people as its chief task’.

The Nazis were as good as their word. While Stalin’s Red Army seized Eastern Poland, the Western, German-occupied half was immediately subjected to a reign of terror unparalleled in European history.

In the first month alone, an estimated 200,000 Poles were killed in savage bombing raids, with hundreds of towns pummelled mercilessly by the Luftwaffe.

Female prisoners are led away for slave work in the German Reich, at the Auschwitz concentration camp, near Krakow, Poland

Meanwhile, as the German tanks rolled east, tens of thousands of politicians, civil servants, landowners, clergymen and intellectuals were rounded up and executed.

In the forest glade of Palmiry, near Warsaw, the Nazis dug mass graves for at least 1,700 politicians, industrialists, teachers and priests.

Anybody who had enjoyed any success was a target: one victim was the runner Janusz Kusocinski, who had won gold at the 1932 Olympics, while others were cyclists, actresses, painters and writers. As Hitler himself had put it, the aim was to destroy Poland’s political and cultural elite for ever.

But even unremarkable ordinariness was not enough to save Poland’s men and women. Entire villages were depopulated or taken hostage, and when the Poles tried to fight back, the Nazis simply murdered them.

According to Polish sources, the total number of villagers killed in so-called pacification exercises approached 20,000, while more than 500,000 farms were burned and eight million cattle and horses were slaughtered.

Yet the terrible fact is that staying alive was little better than dying instantly. Almost immediately, the Nazis began cleansing entire areas to make way for incoming Germans, with a staggering 2.5 million Polish men, women and children forced from their homes.

Many died of exposure, hunger and disease on the roads. The survivors were often herded into the 430 prisons, camps and detention centres established across Nazi-occupied Poland.

An elderly Jewish woman stands on the loading ramp at Auschwitz Concentration Camp near Oswiecim, Poland, 1943/1944

There, thousands were executed. Indeed, 200 Poles were killed in the first inhuman experiments to discover the effects of Zyklon B gas, which was later used against Europe’s Jews in the Holocaust.

Hundreds of priests died in grotesque medical procedures, while at the Ravensbruck camp, 74 young Polish women were killed in horrific experiments that saw their nerves cut, their tissues mutilated with glass and their bones deliberately fractured.

But the horror did not end there. Another three million Poles were forcibly transported to Germany as slaves, where they toiled unceasingly to serve Hitler’s war machine.

Banned from using public transport or fraternising with Germans, they had to wear purple ‘P’ badges and were forced to live in special concentration camps in wretched conditions.

Among the groups chosen for slave labour, one stands out. Soon after the invasion, the Nazis began rounding up thousands of teenage girls and young women, some as young as 15, to work as sex slaves in military brothels.

A Swiss Red Cross driver reported that in Warsaw in 1942, he had seen Nazi soldiers assaulting Polish women in the street.

‘The youngest is maybe 15 years old,’ he wrote. ‘They open her coat and start groping her with their lustful paws.’ One soldier said: ‘This one is ideal for bed.’

As for Poland’s Jews, their fate, so dreadful that words can never do it justice, is horribly well known.

To the Nazis, the Jews were the ultimate enemy, destined only for destruction. Warsaw’s ghetto was the largest in all the Nazi empire, with almost half a million people crammed into an area little more than a square mile in size.

By the end of the war, more than nine out of ten Polish Jews — a staggering three million people — had been killed in the Holocaust.

You may well think, of course, that no amount of money could possibly compensate for such human horror, which is true enough. Some of Poland’s losses, though, were more obviously quantifiable.

The destruction of its cultural heritage, for example, beggars belief.

Polish sources estimate that the Nazis destroyed millions of books, while the historian Dariusz Matelski has worked out that the German occupiers stole a staggering 11,000 Polish paintings, 2,800 European paintings, 1,400 sculptures, 75,000 manuscripts, 25,000 maps, 22,000 antique books and 300,000 antique prints.

Among the 63,000 works still missing are paintings by Raphael, Rembrandt, Rubens, Durer and van Dyck. Some are probably still hidden in the archives of Russian museums, having been looted by the Red Army; others were doubtless destroyed for ever.

The wider economic damage, however, is almost impossible to measure. While hundreds of villages were razed to the ground, the national capital, Warsaw, was almost completely destroyed during the Nazi repression of the doomed Polish Uprising in the summer of 1944.

The city’s magnificent libraries were burned, its palaces obliterated, its public spaces shattered. By the time the Soviet army entered the city in January 1945, the Germans had destroyed 90 per cent of Warsaw’s buildings.

Of course it was rebuilt afterwards at a staggering cost, with the Old Town meticulously reconstructed, brick by brick. Even so, it has never recovered its former glory.

The tragedy, though, is while all this was bad enough, there was still more suffering to come.

Though Britain and France had declared war on Germany to save Poland, the war ended with the Poles enslaved by yet another tyrannical dictatorship — this time, Stalin’s Soviet Union.

Not until the Eighties, when the Solidarity social movement dealt the first real blows to Soviet Communism, did Poland begin to regain its freedom and its pride.

So it is no wonder that even today, many young Poles still feel bitter about their country’s fate —especially when they see their high streets invaded by German businesses, or when they cross the border to see their German neighbours cruising past in their expensive cars.

In Berlin, the Germans are understandably handling the issue of this demand for reparations with great caution.

While Angela Merkel’s spokesman maintained that Germany would face its responsibility for the war, ‘politically, morally and financially’, he was also careful to point out that ‘the question of German reparations for Poland was dealt with conclusively in the past, legally and politically’.

A shawled woman walks down a street in Warsaw through a scene of desolation

If I were Polish, I suspect that I might well echo Jaroslaw Kaczynski’s demands for financial redress. Yet, as an outsider and a historian, I am very wary of the argument for reopening the reparations issue.

If Mrs Merkel did agree to Poland’s demands, where would it end? Who would be next?

Would the Greeks, for example, suddenly discover that they, too, had been insufficiently compensated for the wrongs of the past?

(Many of the furious Greek protests against draconian German financial strictures in recent times referred to atrocities the Nazis carried out on thousands of Greeks during the war.)

Why stop there? After all, there are plenty of countries around the world that might relish the thought of seeking payments from their former masters, which could easily see Britain facing massive financial demands from its old territories.

But the really striking thing, it seems to me, is that this debate has resurfaced at all.

After all, this year marks the 60th anniversary of the Treaty of Rome — the foundational moment in the history of the EU, the organisation that was supposed to have banished memories of World War II for ever.

What is now very clear, however, is that the nationalist passions of the past have not gone away.

Far from wiping the slate clean, globalisation, austerity and mass immigration have reawakened the old resentments, not just in Poland, but in neighbouring countries such as Slovakia and Hungary, too, where migrants from the Middle East have been treated with open hostility.

Indeed, my suspicion is that Mr Kaczynski’s real aim is not so much to heal the scars of the past as to fire a shot across the bows of the EU. Like many of the new nationalists who have come to power across Central and Eastern Europe, he is determined to assert his own independence from what he sees as the interfering busybodies of Brussels and Berlin.

So while I would be very surprised if Mrs Merkel gives the Polish demands more than a moment’s consideration, I would be even more surprised if this is the last we hear of them.

The ghosts of history are not easily silenced, and beneath the pieties that so often pass for political discourse in Europe today, the old monsters may well be waking up.