The Electrical Inspection Directorate (EID) stems from two roots; the older one started in 1889 when it was finally decided to divorce inspection from the other supply functions. Separate inspection departments were created and one, the Inspectorate of Royal Engineer Stores (IRES), became responsible for all technical supplies required by the Royal Engineers, then the main technical corps of the Army. IRES was the older ancestor of EID.
During the First World War period, offshoots from the Royal Engineers became the Royal Corps of Signals and the Royal Flying Corps. Signals needs were looked after by IRES which became the Inspectorate of Engineer and Signals Stores (IESS) while a new inspectorate was formed in 1913 to look after the RFC (later RAF) needs and became the Aeronautical Inspection Department (AID).
During the Second World War the responsibilities of IESS were extended to include radar and also wheeled vehicles and the title became the Inspectorate of Electrical and Mechanical Equipment (IEME). Towards the end of the war responsibility for vehicles was transferred to another inspectorate. In the 1958-9 reorganisation IEME lost its responsibility for mechanical equipment (bridges, pumps, compressors, etc) and acquired from AID responsibility for the electrical/electronic equipment of aircraft. This formed the second root of the present EID which, together with the reorganised AID, formed the Inspection Division of the newly-formed Ministry of Aviation (MOA).
The head of the division was the Director-General of Inspection (DGI). The division was responsible for the inspection of all MOA procurement in the fields of aircraft, atomic weapons, guided weapons and space projects for the Navy, Army and Air Force and for most other electrical/electronic equipment and supplies for the Army. As previously stated, EID's activities were specifically in the fields of electrics and electronics but in the case of atomic weapons EID covered the whole. In the fields mentioned EID was recognized as the inspectorate of ultimate reference.
The title of the directorate derived from a Ministerial decision taken in 1957 and implemented in 1958-1959, to reorganise the five inspectorates of the then Ministry of Supply on a technique basis, as a result of which EID became responsible for the inspection of electrical and electronic equipment and related supplies procured for the Army and the Air Force and for similar items procured for use in Naval aircraft.
EID had four main divisions: Atomic Weapons, Electronics, Engineering Services, and Power and Instruments.
In 1967 EID and AID became parts of the Inspection Division (Aviation Group) of the Ministry of Technology. When that Ministry became part of the Department of Trade and Industry, in 1970, its defence functions transferred instead into the Ministry of Aviation Supply (MAS), but not for long. On 1 May 1971 the MAS was wound up and those defence functions finally transferred into the Ministry of Defence's new Procurement Executive organisation.