This review article focuses on the latest achievements in the creation of a class of electrotuneable optical metamaterials for switchable mirrors/windows, variable colour mirrors, optical filters, and SERS sensors, based on the voltage-controlled self-assembly of plasmonic nanoparticles at liquid/liquid or solid/liquid electrochemical interfaces. Practically, these experimental systems were navigated by physical theory, the role of which was pivotal in defining the optimal conditions for their operation, but which itself was advanced in feedback with experiments. Progress and problems in the realisation of the demonstrated effects for building the corresponding devices are discussed. To put the main topic of the review in a wider perspective, the article also discusses a few other types of electrovariable metamaterials, as well as some of those that are controlled by chemistry.