Historian Richard Van Emden has uncovered the story of how captain Robert Campbell was freed by the German Kaiser so he could visit his dying mother.

The Daily Telegraph reports how the 29-year-old Campbell was captured at the battle of Mons in 1914 and had spent two years in the Magdeburg prisoner of war camp when he heard his mother, Louise, was dying of cancer.

He wrote to Kaiser Wilhelm II, asking to be allowed home to visit her. The German monarch was moved by his story and allowed him two weeks’ leave, on the condition he gave his word as a gentleman that he would return when his time was up.

Van Emden told the Telegraph: ‘Captain Campbell was an officer and he made a promise on his honour to go back.

‘Had he not turned up there would not have been any retribution on any other prisoners.

‘What I think is more amazing is that the British army let him go back to Germany. The British could have said to him: “You’re not going back, you’re going to stay here.”‘

‘I think it is such a unique example that I don’t think you can draw any parallels. In my experience this is a one off.’

Captain Campbell was serving with the 1st Battalion, East Surrey Regiment when he was captured in August 1914.

Freed from captivity in 1914, he returned home and retired from the military in 1925.

He rejoined in 1939, taking up the role of chief observer of the Royal Observer Corps on the Isle of Wight for the duration of World War II.

He died in July 1966 aged 81.