Results achieved by a direct optical link between torus and remote instruments designed for the active phase of JET are reported. The system is based on a labyrinth light path and a set of remotely controllable relay mirrors avoiding a direct view of the plasma core thus reducing the number of neutrons scattered into the detection path. Similar labyrinth systems are presently discussed for next-step fusion experiments with appreciable radiation levels inhibiting the use of fibres in the immediate neighbourhood of the torus. The JET mirror-link covers a spectral range from 2000 to 8000Å which extends considerably the range accessible by standard fibre­-links. The suitability of dominant UV charge exchange spectra for routine ion temperature and ion density diagnostics is addressed by comparing UV and visible ex spectra of eVI, BeIV, Hell and NeX which represent the main light impurities in a JET plasma. As a general rule it is found that the gain in the increase of atomic emission cross-sections for UV ex lines compared to their twins in the visible range is offset by the presence and intensity of additional edge emission lines in the same spectral neighbourhood. The exception of this rule is the UV ex spectrum of BeIV at 2530Å which is characterised by only a few background spectral lines and which offers a straightforward spectral analysis. In the case of the intense, but complex, evI UV spectrum at 3434Å atomic modelling of line ratios has led to a successful reduction of free parameters and to the extraction of ion temperature values consistent with independent measurements.