It reveals that on the day the Second World War began, the former prime minister simply marked the date with the entry scrawled in pencil: "War declared."
It is part of the year-long Outbreak 1939 exhibition at the Imperial War Museum, marking the 70th anniversary of the start of the war on 3 September 1939.
In a letter to his sister, dated a week after Britain declared war on Germany, Chamberlain, pictured, who was in power from 1937 to 1940, described life as "one long nightmare". He wrote: "Of course the difficulty is with Hitler himself. Until he disappears and his system collapses there can be no peace."
The exhibition runs from Thursday.Reuse content