Neville Chamberlain’s diary from 1939 is to go on public display, with the day the bloodiest conflict in human history began marked with a simple entry scrawled in pencil: “War declared.”

The diary is part of the year-long Outbreak 1939 exhibition at the Imperial War Museum in London, marking the 70th anniversary of the start of the Second World War on September 3 1939.

A letter from Chamberlain - who a served as an MP for Edgbaston, Ladywood and was a Lord Mayor of the city - was dated a week after Britain declared war on Germany shows the strain of struggling to maintain peace in Europe in the face of Hitler’s belligerence.

The then-prime minister wrote to his sister describing life as “one long nightmare” and acknowledging there was no hope for peace while Hitler was in power.

“Of course the difficulty is with Hitler himself. Until he disappears and his system collapses there can be no peace,” he wrote.

Outbreak 1939 explores the build-up to - and preparations for - war and gives an overview of the key events of September 3 and the early months of the conflict.

Other highlights include the then-foreign secretary Lord Halifax’s letter to Germany formally declaring war, the jacket King George VI wore as he broadcast to the nation on the evening the war began, and a medal awarded to Thomas Priday, the first British soldier to be killed in action.

An ITV1 documentary also called Outbreak 1939, featuring interviews with famous faces giving their memories of the start of the war, will be screened on September 3.

Tony Benn, Vera Lynn, Betty Driver, Nicholas Parsons and Peter Blake are among those to feature in the programme.