“History will be kind to me,” predicted Winston Churchill, “because I intend to write it.” And so it proved. Churchill’s The Second World War, which began to appear in 1948, largely set the agenda for all subsequent presentations of the war years, especially in western countries: Britain stands in the centre of the conflict and her survival paves the way for victory.

As Churchill has it, Britain’s enemies, the axis powers, provide the sole authors of aggression, of criminal conduct and of undefined “evil”. The tide turns at El Alamein. Britain’s principal allies, the US and the USSR, which Churchill brought together in the grand coalition, provide the twin sources of military muscle that hunt down the fascist beast.

In Europe the allies of east and west co-operate, overcome their differences and triumph. The spectacular landings of the western armies in Normandy match the huge “Russian” successes on the eastern front. The Reich is crushed. Freedom and democracy prevail and “Europe is liberated”.

Unfortunately, the truth is more complex. The Russians, for example, are clear that the Red Army played the dominant role in the defeat of the Reich, demoting the Anglo-American war effort to secondary or tertiary importance. What is more, like the Americans, they insist that the “real war” began in 1941, relegating the events of 1939-41 to a mere prelude. For their part the Americans are most conscious of the competing demands of the two theatres of action in Europe and in the Pacific. They also emphasise the importance of the US as “the arsenal of democracy”.

Any attempt to revise established views provokes resistance, although I must admit to being surprised at the vehement opposition I encountered when challenging the Churchillian version. Other historians, such as Richard Overy, Robert Conquest and Anne Applebaum, have been peeling away the layers of myth for the past four decades, but still many people are unwilling to judge events on their own merit for fear of being accused of supporting “the forces of evil”.

Others recoil with incredulity from the notion that our patriotic opinions about 1939-45 may constitute something less than the whole truth. Both the British and the American public have long been told that “we won the war” and D-Day, in particular, has been built up as the decisive moment. The American D-Day Museum has been adopted as the national tribute to the war and Steven Spielberg, the director of Saving Private Ryan and co-producer of Flags of Our Fathers, which is just about to open, seems to have made it a mission to perpetuate Churchill’s myth.

After talking at Cambridge recently about the preponderance of the eastern front and the scale of the Red Army’s triumph, I was accosted by an angry young British historian. “Don’t you realise that we were pinning down 56 German divisions in France alone,” he said. “Without that the Red Army would have been heavily defeated.” What is less acknowledged is that without the Red Army pulverising 150 divisions, the allies would never have landed.

The attack on the Third Reich was a joint effort. But it was not a joint effort of two equal parts. The lion’s share of victory in Europe can be awarded only to Stalin’s forces and it is a fantasy to believe that he was fighting for justice and democracy.

Separating the facts from the myths and the propaganda is not easy. One of the trickiest problems in establishing a credible narrative of the war arises from the misconception that the largest combatant state, the USSR, stayed neutral before the German attack of June 1941. Soviet accounts have always preferred to focus on the so-called Great Fatherland War, and carefully avoids close examination of Stalin’s political and military machinations in the preceding years.

Western commentators have usually followed this line, reluctant to publicise their embarrassment at Hitler’s initial partner becoming the ally of the democratic West.

In reality, in the first 22 months of fighting when the Wehrmacht attacked and occupied eight countries, the Red Army attacked and occupied five. These manifest aggressions make nonsense of any claims of neutrality or of defensive responses to the provocations of others. In November 1939, for example, Stalin’s unprovoked invasion of Finland resulted in a war that lasted for twice as long as any of Hitler’s early campaigns.

Similarly, the Soviet annexation of the Baltic states in 1940 was no mere “strengthening of the defences” or “readjustment of frontiers”. It was a brutal act of depredation that destroyed three sovereign European states, together with a quarter of their population. All these events were facilitated by the Nazi-Soviet pact, which gave Stalin the same licence for banditry in the Soviet sphere that Hitler was exploiting in the German.

Proportions, however, are crucial. Since 75%-80% of all German losses were inflicted on the eastern front it follows that the efforts of the western allies accounted for only 20%-25%. Furthermore, since the British Army deployed no more than 28 divisions as compared with the American army’s 99, the British contribution to victory must have been in the region of 5%-6%. Britons who imagine that “we won the war” need to think again.