Jones was born on 1 November 1895 in Arabin Road, Brockley, Kent, now a suburb of South East London, and later lived in nearby Howson Road. His father, James Jones, had been born in Flintshire in north Wales, to a Welsh-speaking family but was discouraged from speaking Welsh by his father, who, in common with many Welsh-speaking parents of the time, believed that habitual use of the language might hold his child back in his career. James Jones had moved to London to work as a printer's overseer for the Christian Herald Press, and it was here that he had met his wife, Alice, a Londoner born and bred. They had three children: Harold (who died at 19 of tuberculosis), Alice, and David.