Harold William Clayden, son of Edward John Clayden and his wife Eliza Ann, who was also born Clayden, commenced his engineering training at Faraday House, London, in 1890. Subsequently he held junior positions in borough power stations at Eastbourne and Coventry. He was an associate member of the (British) Institution of Electrical Engineers and from 1908 also an associate member of the (British) Institution of Mechanical Engineers. In 1897 he became borough electrical engineer to Morley Corporation, Yorkshire, and the next year joined the staff of Mr Robert Hammond, consulting engineer of London. In 1899 he was appointed borough electrical engineer to the Corporation of Middlesbrough, Yorkshire. In 1902 he married Florence Hilda Richardson, with whom he had two sons and three daughters.
Also in 1902 Clayden came to South Africa to take up an appointment as chief mechanical and electrical engineer to the Consolidated Main Reef Mines and Estates, Ltd. at Maraisburg (now part of Johannesburg). He held this position until 1914, when he became consulting electrical engineer (from 1919 consulting electrical and mechanical engineer) to the General Mining and Finance Corporation, Johannesburg. He also served on many committees of the South African Chamber of Mines.
Clayden was concerned mainly with the application of electricity to mining on the Witwatersrand. He was a member of the South African Institute of Electrical Engineers, serving as its president for 1925/6. His presidential address dealt with "Electricity as applied to mining". Two other papers by him that appeared in the institute's Transactions were "Some notes on efficiencies and costs of steam and electric winding plant" (1916) and "Power supply on the Rand, from the standpoint of the mining consumer" (1919).
Clark became a member of the South African Association for the Advancement of Science in 1916, and a member of the Chemical, Metallurgical and Mining Society of South Africa in 1920.