This paper provides details of accelerated irradiation experiments on a Magnox mild steel submerged-arc weld at mean irradiation temperatures of 165°C and 269°C. The irradiation-induced changes in mechanical properties and weld microstructure have been determined. Irradiation increased the 40J transition temperature and the yield stress. The increase in transition temperature at a given dose was rather higher in the lower temperature irradiations. Irradiation-induced precipitates of about 2nm diameter were produced in both series of irradiations. Small angle neutron scattering data indicated a precipitate composition of about 75Cu25Mn (at%). Electron microscopy confirmed the presence of copper-rich precipitates of that size. The irradiation dose ranges covered the development stage of the precipitation. The directly measured and (yield stress) derived transition shift data were interpreted satisfactorily using a mechanistically based model involving a matrix damage component and a component attributable to copper precipitation.