British infantrymen during the Battle of the Somme. Almost a million British soldiers died in the Great War Credit: PA Wire/Press Association Images

A British soldier voluntarily returned to a German prisoner of war camp, after he was allowed home to visit his dying mother during World War One, a historian has discovered.

Captain Robert Campbell, aged 29, was captured by German authorities only two weeks after Britain declared war on Germany in July 1914, and imprisoned in Magdeburg prisoner-of-war camp.

When he heard his mother was gravely ill, he wrote to Kaiser Wilhelm II asking to be allowed to visit her in England.

His request was granted and he returned to his family home in Gravesend in December 1916 to spend a week with his mother, who was suffering from terminal cancer. He returned to the camp and stayed there until the war ended in 1918.