Understanding the effects of neutron irradiation of materials is one of the outstanding issues in the development of fusion technologies. The impact of this work derives from the opportunity, for the first time in a tokamak operating with a D-T plasma, to deliver experimental results which directly link to the nuclear characteristics of real samples of ITER structural materials, and importantly their inherent impurities, exposed to neutrons in this unique environment. The experiments planned for 2020 at JET, notably including a D-T experimental phase, are expected to produce large neutron yields, in the region of 1021 neutrons. The scientific objectives are linked with WPJET3, a programme to deliver the maximum scientific and technological return from those operations. Significant results have been obtained to date with a focus on relevance to ITER device operations. The nuclear activities that have been performed include the 14 MeV calibration of neutron yield monitors, neutronics benchmark experiments, nuclear diagnostics and data processing for tritium breeding blankets, and activation measurements with supporting analyses for fusion materials. The latest results from experimental activities conducted within the `ACT’ subproject under WPJET3 are discussed, including gamma spectrometry measurements of post-irradiated samples following JET campaigns, where samples have been irradiated in a long-term irradiation station (LTIS) assembly and via the JET pneumatic sample transfer system. The characterisation and neutron spectrometry approach used is described, extending on our previously published work in. Experimental results are compared to simulations performed using the MCNP6 with FISPACT-II nuclear codes. Validation of such simulations are important since they are applied extensively to predict a wide range of nuclear phenomena, such as gamma activation fields, associated with components and materials that will be used in ITER operations. Our plans to experimentally study radiation-induced defects generated in post-irradiated W, Mo and Fe samples via the Positron-Annihilation Lifetime Spectroscopy technique are also detailed.