In the JET tokamak, the perpendicular velocity distribution function of minority ICRF-heated protons in the MeV energy range is inferred from neutral particle analyzer (NPA) measurements of the emitted hydrogen flux, integrated along a vertical line-of-sight through the plasma centre. In particular, the best-fit perpendicular tail temperature ~T⊥ of the inferred distribution can be determined with good accuracy. In this paper a relation is established between the measured quantity ~T⊥ and the perpendicular tail temperature T⊥(0) of the heated protons at the position of maximum ICRF power deposition. If measurements are made at energies E which lie well above T⊥ (O), the value of  ~T⊥ inferred from the NPA measurements is only slightly lower than T⊥(O). In the opposite limit E<< T⊥(O), it is shown that ~T⊥ << T⊥(O). When this model is applied to NPA measurements from a JET pulse with varying levels of applied ICRF power PRF, it is found that the scaling of T⊥(0) with PRF in the 2-10MW range is almost exactly linear, as expected from the widely-used Stix model. Moreover, calculated values of the ICRF­heated proton energy content, based on deduced values of T⊥(0), are in agreement with independent diamagnetic measurements of the energy. These results validate the model of impurity-induced neutralization of MeV protons which has been developed to interpret NPA flux measurements in JET. The measurements thus give access to a fundamental property of the high energy minority proton energy distribution, which plays a crucial role in theories of sawtooth stabilization. The successful measurement of ICRF-heated proton distributions in the high energy range gives confidence that the NP A instrumentation, and the interpretation techniques described here, could provide valuable data on the behaviour of fusion products in forthcoming deuterium-tritium experiments in JET.