  We present deep, narrow-band and continuum images of the powerful z=0.811
radio galaxy 3C265, taken with the TTF on the WHT, together with detailed
long-slit spectroscopic observations along the axis defined by the UV/optical
emission elongation. The deep images reveal the existence of cones in the
ionization structure within ~7 arcsec (58 kpc) of the nucleus, where the
emission-line structure is not closely aligned with the radio axis. This
indicates that anisotropic illumination from the central AGN dominates on a
small scale. At larger distances (>10 arcsec) from the nucleus, low-ionization
emission gas is closely aligned with the radio axis, suggesting that jet-cloud
interactions may be the dominant mechanism in the line-emitting gas on a larger
scale. Moreover, the presence of a high-velocity cloud at 2.5 arcsec from the
nucleus, close to the radio axis, indicates that even close to the nucleus
jet-induced shocks have an important kinematic effect. While on a large scale
the low-ionization emission-line structures are aligned with the radio axis, on
a smaller scale, where AGN-photoionization dominates, the highest surface
brightness structure is aligned with the closest companion galaxy. This suggest
that much of the emission-line structure reflects the intrinsic gas
distribution, rather than the ionization pattern imprinted by the radio jets or
by AGN illumination. Overall, our results underline the need for a variety of
mechanisms to explain the properties of the extended emission-line gas of radio
galaxies (abridged).
