LAURENCE REES: And so Stalin then finds himself in a paradoxical situation, since he starts offering military assistance - for example, in the form of a naval supply base north of Murmansk - to the Germans. The very people he thinks eventually want to attack him.

SIMON SEBAG-MONTEFIORE: Yes.

LAURENCE REES: He’s also giving them huge amounts of oil, huge amounts of grain and so on.

SIMON SEBAG-MONTEFIORE: Yes, it is a huge paradox. It’s a huge gamble and risk, but it’s the sort of gamble that Stalin thinks he understands in a very old-fashioned way. In his library he has all these books on 19th Century German history, the Prussian history, including books on Bismarck and stuff. I’ve seen all these books in his library, and it was just unthinkable to him that anyone would make that mistake of having a war on two fronts. As far as he was concerned, Germany would never attack because they would get stuck. First of all, he made what he regarded as a brilliant deal. It was too good, and that should have made him suspicious - the fact that Hitler at that point was willing to give him everything that he asked for. They held back very little. It was Finland, the Baltic States, East Poland, Moldova, all the way down. So they gave him this huge strip of territory and again, as someone who thought completely in this Russian Tsarist imperial way, this was all he wanted.

He loved looking at the map with his pipe and reviewing it and saying, yes, not bad, we’re safer, but he was thinking in an old-fashioned pre-Blitzkrieg way because, of course, that territory could just be covered in a few days by tanks and could be flown over by Stukas instantly. So it was less of a success than he thought. He thought that then they would swallow Poland but that would just be a partition, one of the 18th Century partitions, and then of course Hitler would get stuck in a huge war, probably with trenches on the Western Front. France had one of the biggest armies in Europe and Britain was the British Empire, so of course Germany would not be able to beat both of them.

So that was all taken care of, and it would be years before they turned to Russia, and by then they might be exhausted and they would never turn unless both Britain and France were defeated. So that all made sense, so he was just buying time with all these natural resources. And as he often said to people, Russia’s not like any other country; we are so colossal. No one would invade us, we can afford all these mineral ore resources to give away. And of course things didn’t turn out as he expected. He basically got it totally wrong.