Were Churchill and Roosevelt as friendly as legend would have us believe? Was it necessary for the British and the Americans to surrender so much to Stalin at Yalta? Did the British behave honourably towards the wartime Poles? Was Stalin's wartime conduct in any way less morally repugnant than that of Hitler?

These are some of the questions considered by Laurence Rees in a new BBC television series, for which he has written an accompanying book. The author, who created a memorable series on Auschwitz, now seeks to address some less familiar issues of the second world war, throwing light upon its darker nooks and crannies.

Much of the book is based upon material from Soviet archives and fresh testimony from veterans. There are vivid stories about Russians who lived in Murmansk in the days when Arctic convoys docked there. British sailors who ventured ashore met implacable official hostility and startling manifestations of Soviet ruthlessness. One of them, Eddie Grenfell, describes how a drunken Russian petty officer one night appeared at the barracks doors, only to be dragged away by sentries. A commissar appeared shortly afterwards and apologised to the British visitors: “We are sorry you were disturbed like this. It was dreadful that this man should have behaved as he did. You'll be glad to know we shot him.”

Russian women, by contrast, embraced the British with enthusiasm when they had the chance. Valentina Ievleva fell in love with a sailor, and implored him to make love to her: “Bill, I want to have your baby, because I'm not going to love anyone any more.” The sober young man replied: “Val, you're a good girl, I don't want to ruin you. I believe in God and I don't want to be responsible for your ruined reputation.” Valentina told Rees: “I was very hurt by what he said, because I wanted to be a woman...A Russian wouldn't have...well, wasted his time in such a way.”

Most of Rees's book, however, addresses larger and graver issues. He discusses the monumental cynicism of the Nazi-Soviet Pact in August 1939, which precipitated war. Stalin said: “If...Germany finds itself in a difficult situation, then she can be sure that the Soviet people will come to Germany's aid and will not allow Germany to be suppressed. A strong Germany is in the interests of the Soviet Union.” At the signing ceremony, the Russian warlord himself filled the champagne glasses of German diplomats, and proposed a toast: “Because I know how much the German people love their Führer, I want to drink to his health!” Rees suggests that, if Hitler had sought active military assistance from Stalin, this might have been forthcoming. In June 1941, when the German ambassador called on Molotov to deliver a declaration of war, the shocked Soviet foreign minister said: “Surely we haven't deserved this.”

The book discusses at length Britain's dealings with Russia over Poland, noting that the government was much less robust than is sometimes thought about Polish territorial integrity. Poland's borders, shrugged the Foreign Office as early as 1939, were “fluid”. After initial hesitation, both Churchill and Roosevelt became astonishingly willing to redefine them in Russia's favour, to discourage Stalin from seeking a separate peace with Hitler.

Rees rehearses the shocking saga of Stalin's 1939-40 massacres of the Polish elite, now believed to total 21,857 victims, in addition to 300,000 deported to the Gulag. Later, when Poland's General Anders charged Stalin with the fate of several thousand Poles unaccounted for, and presumed to be held in captivity somewhere in the Soviet Union, Stalin replied blandly: “That is impossible. They have escaped.” The incredulous Anders demanded, where to? “Well,” shrugged Stalin, “to Manchuria.”

Owen O'Malley, the British ambassador to Poland's exiled government in London, wrote a brilliant dispatch, discussing the government's brutal decision to suppress knowledge of the Polish massacres in the interests of the vital Soviet alliance: “In handling the publicity side of the affair...we have been obliged to appear to distort the normal and healthy operations of our intellectual and moral judgments; we have been obliged to give undue prominence to the tactlessness or impulsiveness of the Poles, to restrain the Poles from putting their case clearly before the public, to discourage an attempt by the public and the press to probe the ugly story to the bottom.”

Roosevelt, whose relations with Churchill were much less cordial than popular myth suggested, was never much interested in eastern Europe, or Poland in particular. He was delighted by Stalin's willingness to support his cherished plan to create the United Nations, and went far beyond the demands of diplomacy in praising the Soviet leader. “I may say that I ‘got along fine' with Marshal Stalin,” he told America in a 1943 Christmas Eve broadcast, following the “Big Three's” Tehran summit. “He is a man who combines a tremendous relentless determination with stalwart good humour. I believe he is truly representative of the heart and soul of Russia; and I believe that we are going to get along very well with him and the Russian people - very well indeed.”

Rees argues that, given Russia's desperate need for American supplies and later desire for its cash, Roosevelt could have applied far more pressure to the Soviet Union about, for instance, Poland. And if Britain's prime minister was more alive to the perils of Soviet expansionism, he made the same mistake as the US president, in supposing that he might forge an emotional connection with Stalin.

Among the book's considerable anecdotal evidence from Russians and Poles about their war experiences are accounts of relatively unfamiliar horrors, such as the Red Army's February 1945 storming of Budapest. An orgy of rape took place, which anticipated later events in Berlin. In one incident, recounted by a Hungarian named Ivan Polez, Russian soldiers found a 17-year-old maid in a cellar crowded with terrified people. “Please help me! Help me,” the girl cried, as they dragged her forward. Polez said: “Everyone was frozen - stone. This was a terrible moment. And then the owner of the house, a retired military officer, started to talk to the maid. He said: ‘Please make this sacrifice for the sake of the country. And with this you will be able to save the other women here who will never forget this.'” The Russians dragged the girl upstairs. Later, she was thrown back into the cellar, sobbing and appallingly injured. The others in the cellar, in Polez's words, “didn't even dare to look at her”. An estimated 50,000 Hungarian women were raped in Budapest.

The coherence of the narrative suffers a little from addressing so wide a subject in episodic fashion. But Rees is vastly well informed about the second world war. His judgments can seldom be faulted. It is foolish to expect revelations about this period from any of us who write about it today, because almost all sensational claims prove nonsense. But there are many surprises here, and much good detail.

Rees's principal message is that the allied cause was inescapably and deeply compromised by association with the bloodstained Soviets, morally indistinguishable from the Nazis. The West had no alternative save to make common cause with Stalin. The Soviets paid the blood price necessary to defeat Hitler's legions. Had they not done so, British and American soldiers might have filled cemeteries as large as those of the first world war. The relationship between Stalin, Roosevelt and Churchill makes an ugly story, and Rees tells it extraordinarily well.

World War Two by Laurence Rees
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