This work is carried out as continuation of fast ion research on JET due to its significance for the future JET operation with ITER-like Be wall and ITER. Fast ion studies on JET aiming at assessing the peak values of fast-ion losses caused by plasma disruptions, TAE, and NTM are performed. Gamma-ray diagnostics, NPA, neutron spectrometry, Faraday Cups and Scintillator Probe were used for simultaneous measurements of various species of confined and lost fast ions in the MeV energy range. The fast ion populations were generated in fusion reactions and were also produced by NBI and by accelerating with ICRH. Significant fast ion losses preceding disruptions were often detected by Scintillator Probe in discharges with high bN. It was found that the losses are caused by the m = 2/n = 1 kink mode and these losses typically occur at the same time as the thermal quench before the current quench that follows. A set of experiments were carried out where interactions of core-localised TAE modes with fast ions in the MeV energy range were studied in plasmas with monster sawteeth. Energy and pitch angle resolved SP measurements of MeV-ions ejected from the plasma due to fishbone oscillations driven by NBI-ions are also studied. Experiments using RMP ELM control have exhibited a strong effect of EFCC on NTM and on NTM-induced losses of NBI ions.