Tredomen Engineering Works, south Wales, was founded by Powell Duffryn Ltd in 1922, and was rested in the National Coal Board (NCB) at nationalisation in 1947. It was controlled by the South Western Division of the NCB until 1966 when it became a headquarters activity. In 1973 it was incorporated as a subsidiary of the NCB (Ancillaries) Ltd. From 1985 control passed to the Technical Director until it was sold in 1988.
[Source, National Archives, http://discovery.nationalarchives.gov.uk/details/r/C5334, accessed 18 Dec 2017]