LAURENCE REES: Let's talk about the relationship with Stalin. At the beginning of 1942 Churchill is absolutely outraged at the notion that we would hand over eastern Poland to Stalin at the end of the war. Then, less than 2 years later at the Tehran conference Churchill volunteers to cooperate in the Soviets snatching this territory. Why this gigantic shift? 

ANDREW ROBERTS: The massive shift takes place solely because the Red Army starts to fight back. In the period when over 3 million Russians go into captivity - they have half of their air force knocked out in the first 48 hours after Operation Barbarossa is unleashed - when 100s and 100s of miles are lost and the Germans get within a few miles of Moscow, one can understand why the general staff in the West and certainly the politicians in the West and primarily Churchill and Roosevelt have no time for Stalin. They have something approaching contempt for a country that is being so comprehensively wiped out. By the time in December 1941, when German troops start surrendering to Zhukov on the Moscow Front, and certainly at the time of Stalingrad in late 1942 and most definitely by the time the Germans were unable to win the Battle of Kursk, it becomes clear that Stalin is not somebody who’s about to be pushed off, but instead is going to be commander of the army that finally takes Berlin. And so as a result you can you can plot the increased respect and time that Roosevelt and Churchill have for Stalin on the map of the Eastern Front.

LAURENCE REES: But what Churchill actually says, when he writes a note about this change in policy to Eden after the Tehran conference, is that, yes, the Soviets have won these great victories, but also crucial is the 'changing nature' of Stalin's regime. Did Churchill write that just for the history books?

ANDREW ROBERTS: I think Churchill did say a lot of things and write a lot of things for the history books. He was an historian and he was very careful about what he was going to be able to point to in his volumes upon volumes of memoirs - tremendously well paid memoirs. However, I think that he did allow himself almost as much as Roosevelt to get rosy tinted spectacles with regard to the Soviet regime, even though he’d hated the Soviet regime for years. When he came back from Yalta he told the British cabinet that he understood Stalin, and he could do deals with Stalin and he felt it. I mean the 'percentages' deal in October 1944 was another classic example of Churchill believing that through his force of personality, but also through the British war effort, somehow this was going to have some effect on Stalin. It was a profound misunderstanding of the kind of man that Stalin was and the kind of regime that he ran.

LAURENCE REES: And almost inexplicable because by then he knows about the NKVD arresting former members of the Polish Home Army. So Churchill knows that this whole apparatus of Stalin's terror is coming into Eastern Europe, and then he acts as though Stalin is somebody who we can trust?

ANDREW ROBERTS: I think that there is a certain degree of conning himself, and it’s a mistake to blame Roosevelt as the only naive person towards the Soviets in the allied hierarchy. In fact plenty of people would have wanted to look the other way and wanted to take the easy route. And also at the same time in sheer terms of real politique, what are you going to do if the Red Army has 6 million troops, that are after all fighting incredibly hard in Poland and eastern Germany? It’s Russia all the way up to the Baltic States and all the way down to Romania and Hungary. You know, practically speaking, other than landing a large army in Normandy in June 1944 what can we actually do?

The destruction of Army Group Centre takes place in July and August 1944 which is after the landings in Normandy, and when we’re still trying to capture Caen the Russians are destroying division after division of Army Group Centre. And there is a massive dichotomy here and it’s something that the British and the Americans are very conscious of, as we have not taken on the might of the German Empire, Third Reich, face to face. Four out of every five Germans who die on a battlefield are killed on the Eastern Front and Roosevelt and Churchill know that.

LAURENCE REES: But it’s one thing to know that and another to con yourself about the nature of the person and the nature of that regime, and yet Churchill is doing that?

ANDREW ROBERTS: Yes. I don’t think he ever comes round to saying that he likes Stalin as a person. I think he says that he’s a man who he can do business with.

LAURENCE REES: In the summer of 1942 after Churchill and Stalin's boozy night together, Churchill goes back to his Dacha and says to Clarke Kerr, the British ambassador to Moscow, that he thinks Stalin is a 'great man'. 

ANDREW ROBERTS: Well, certainly in the Burgess Papers at Cambridge, which has the verbatim accounts of the war cabinet meetings, there is one where he returns from Yalta, where there’s nothing in it for him to exaggerate or lie or cheat - the war cabinet after all - plus he doesn’t know that the minutes are going to survive and must have taken it for granted that Norman Brooke was going to be able to make the matter die like most of the rest of the war cabinet minutes. And so there he is hailing Stalin as somebody whose words he believes he can trust on the issue of Polish integrity and independence, though admittedly he is the first person to come round and see that that is impossible, but by that stage he’s out of office.