Born the oldest son of George William and Mary Ann Hedges in Bicester. He became a draper's apprentice in London but joined the medical corps at the outbreak of WW1 by adding six months to his age. He had tunnel vision that would have kept him from active service but was persuaded by his church to register as a conscientious objector. He was posted to Valetta where he became a drill instructor but he found the screams of the injured greatly depressing. His younger brother Cecil died in a swimming accident during army training in 1918. Despite this, Sid went on to write several books on swimming.
After being demobilised in January 1919 he refused to return to the family draper's shop. He took violin lessons to develop the skill that he had learnt in Malta and practiced for 16 hours a day to earn his teaching diploma within 15 months.
His stories did not sell well at first but he persevered until he could support himself entirely by writing.