Sidney left Salford Grammar School in 1930. His early career was as a travelling salesman selling radios around Greater Manchester. It was this experience which drove the young Sidney into politics. Witnessing the living conditions and high unemployment in some areas of Salford, he joined the North Salford Branch of the Labour Party in 1932, aged 18. Sidney would later establish Searchlight Electrics, using his army demobilisation payment to purchase a small factory in Salford in 1945.