the expected detection efficiencies for both electron and nuclear recoils. These studies, supplemented with Monte Carlo simulations using the GEANT4 toolkit [@geant4], have been presented previously [@vetoPaper1]. In the following sections we present the realised performance of the veto detector following six months of continuous operation. We first give a brief description of the system followed by results from calibrations showing detector stability and operational robustness. In the subsequent sections the efficiencies for rejecting coincident $\gamma$-ray and neutron events in ZEPLIN–III are presented. These so-called ‘tagging’ efficiencies are defined as the fractions of events occurring in the xenon target that are successfully identified and may be vetoed. As is described in Section \[gammatagging\], $\gamma$-rays that deposit energy in the liquid xenon and the veto detector do so approximately simultaneously. Consequently, such coincident vetoed events are labelled ‘prompt’ tags. Signals in the veto following neutron recoils in ZEPLIN–III, however, arrive after a time which depends on the passive shielding and veto detector geometry and composition. The majority of these neutron events are well separated in time from prompt tags and, as is described in Section \[neutrontagging\], are labelled ‘delayed’ tags. In Section \[implications\] we discuss briefly how the tagging of a 