Molecular switches on surfaces are intensely investigated because they may provide potential components in molecule-based functional devices. For applications such as data storage on a single molecule level it will be useful to switch a single molecule reversibly in densely packed arrays. External stimuli like light, temperature and electric fields have been used in the past to induce conformational changes but do not provide single molecule selectivity. The current injected from a scanning tunnelling microscope tip is spatially localized to sub-molecular dimensions. Nevertheless, lateral electron transport at metal surfaces appears to prevent addressing of a single molecule in a layer. We use a molecular spacer to suppress this non-local effect and to increase the lifetime of electronic excitations. Single molecule switching is demonstrated in self-assembled layers utilizing the vertical motion of a central ion of a phthalocyanine derivate, thereby eliminating the need for lateral free space within the layer. Switching is achieved via hole or electron attachment. The bistable states of this switch can be clearly discriminated in scanning tunnelling microscopy images and by their high on/off conductance ratio. Using density functional calculations the efficiency of the switching process is interpreted in terms of resonant electron tunnelling to molecular orbitals.