The authors have, in the past, been directly involved in the design, planning and supervision of the construction, of a new ultra-high-voltage laboratory. The main purpose of the laboratory was to provide a major facility in the UK for the development of switchgear rated up to 765 kV and in the dielectric research required for such an undertaking. Following the opening of the laboratory in 1970, the author have in recent years been closely connected in the development of new ranges of open terminal and metalclad SF6switchgear rated up to 525 kV and for fault currents up to 63 kA. These activities have been supported by extensive dielectric research studies, which have enabled the major factors influencing the insulation integrity of practical equipment to be determined. First, this paper outlines the criteria used in designing the laboratory and presents a critical appraisal of the facilities during the first 15 years of operation. Secondly, consideration is given to illustrating some significant laboratory activities. Examples are given of various switchgear and nonswitchgear components for systems ≤765 kV, which have been subjected to rigorous dielectric proving tests in the main test hall. The use of specific high-voltage test procedures (e.g. climatic, artificial rainfall, mixed voltage testing) are described, and important technical factors which have influenced the dielectric design of apparatus are considered.