asked the Secretary of State for Defence what chemical warfare exercises have been carried out since 1945 involving the depositing of zinc cadmium by military aircraft.

Between 1955 and 1963 a research programme was undertaken which involved the dissemination over parts of the United Kingdom of zinc cadmium sulphide in small particles, highly diluted in air. In this form, it is a recognised substance for use in air in the ionisphere which can affect long distance radio communications and can cause marginal depletions to the ozone layer, but these would be restored fairly rapidly by natural processes.