the zero order and B band light curves are reported in the left panel of Fig.5, while the emission line fluxes of SiIV, CIV and HeII are shown in the right panel. The orbital gaps due to the HST sampling are apparent.

A strong colour dependence is encountered in the modulation amplitudes as well as the phasing. Fractional amplitudes range from 40$\%$ in the far-UV to 28$\%$ in the near-UV (IUE band) and 15$\%$ in the optical. The modulation amplitudes then have increased by a factor $\sim$ 2.5 in the UV and $\sim$ 1.5 in the optical with respect to 1990. However, the phasing of UV maximum and minimum has not changed with time, occurring at $\rm \Phi_{orb}=0.86$ and $\rm \Phi_{orb}=0.34$, respectively. The UV modulation is more sinusoidal, whilst the optical light curve is more structured with a double humped maximum between $\rm \Phi_{orb}$ = 0.75 and $\rm \Phi_{orb}$ = 0.0. A comparison with the optical behaviour in 1990 indicates an absence of a broad maximum centered at $\rm \Phi_{orb}$ = 0.0 and a less defined minimum. The current observations are inadequate to resolve the orbital dip due to a grazing eclipse of the accretion disc in either UV and 