When Nazi Germany invaded the Soviet Union on 22 June 1941 it also threw the latter into a temporary alliance with Britain. The implication in this sentence that the alliance was accidental is intentional. Certainly no one would have confidently predicted it even a matter of weeks before the German attack. Anglo-Soviet relations since the Russian revolution of 1917 had never been good, let alone close. Britain had taken a leading part in the futile and misguided allied intervention on the side of the ‘Whites’ in the Russian civil war; diplomatic relations, opened in 1924, were broken off by the British government in 1927 on the grounds of Russian interference in Britain's domestic affairs; and although these relations were restored in 1929, the Soviet Union continued to be the object of suspicion and barely disguised hostility on the part of the right-wing governments which ruled Britain in the 1930s. Russian attempts to build an anti-fascist coalition from 1935 onwards were never taken seriously by these governments, partly because the Red Army was deemed to be capable only of defensive operations – a sentiment heightened by the Stalinist purges of 1936–8 – and partly because it was feared that Russia's Communist rulers were anxious to embroil Britain in a war for their own selfish purposes.

The events of 1939–41 did nothing to modify these sentiments. Indeed, there were now fresh grounds for suspicion and hostility: the Molotov–Ribbentrop non-aggression pact of August 1939 itself, the Soviet occupation of eastern Poland (a corollary of the pact), its invasion of Finland, its annexation of the Baltic States and its supply of raw materials to Nazi Germany.