and roof plug (labelled B and hatched). Surrounding these are the active scintillator modules (C) with PMTs housed in cups and recessed into the lower polypropylene structure. The 20 roof modules of scintillator (D) rest on the roof plug. The lower polypropylene structure (E) contains no Gd and rests on a copper and a lead base (F). Finally, the lead castle (G) envelopes the entire assembly.](cad.eps){width="8.6cm"}

The veto instrument has two main components. A Gd-loaded polypropylene structure, close-fitting around and above ZEPLIN–III, moderates and captures neutrons that may have scattered in the WIMP target; this structure is shown in Figure \[vetofigure1\] during assembly. The capture $\gamma$-rays are detected by 52 plastic scintillator modules (polystyrene-based UPS–-923A) which are assembled around the polypropylene; these are shown in Figure \[vetofigure2\] after assembly. The entire structure is subequently enclosed in a Pb castle, as depicted in Figure \[cad\], a schematic drawing of ZEPLIN–III, the veto system, and passive shielding. A detailed description of the veto detector hardware is given in Ref. [@vetoPaper1], here only a brief summary is presented.

The scintillator modules each have one PMT (ETEL-9302KB) optically coupled to one end. The PMT and associated electronics are housed in a plastic cylinder which 