Soviet dictator Josef Stalin and Britain's wartime Prime Minister Winston Churchill enjoyed an alcohol-fuelled all-nighter in Moscow as World War Two was in full swing, previously secret files have revealed.

Relations between the two leaders were stiff until Churchill arranged a tete-a-tete with Stalin, with the aid of interpreters, which led to a late-night boozy banquet in 1942, according to files released by Britain's National Archives.

"There I found Stalin and Churchill, and Molotov who joined them, sitting with a heavily laden board between them: food of all kinds, crowned by a suckling pig and innumerable bottles," wrote Sir Alexander Cadogan, permanent under-secretary at the Foreign Office, of the visit.

The mood was "merry as a marriage-bell," he added, though Churchill was complaining of a "slight headache" when Cadogan came to find him at one in the morning, and "seemed wisely confining himself to a comparatively innocuous effervescent Caucasian red wine."

The two leaders did not engage in much military talk during the meeting, which went on until three in the morning, but Churchill did probe the Georgian-born dictator about his internal policy.

Asked what was happening with the kulaks, the relatively rich farming class Stalin had vowed to exterminate, he responded "with great frankness" saying that the kulaks had been given land in Siberia but '"they were very unpopular with the rest of the people!"'

The evening was dubbed a success by the author of the note, as the two men got on.

"Certainly Winston was impressed, and I think the feeling was reciprocated," he wrote.