  An analysis of the kinematics and ionisation state of the emission line gas
of a sample of 14 3CR radio galaxies with redshifts z~1 is carried out. The
data used for these studies, deep long--slit spectroscopic exposures from the
WHT, are presented in an accompanying paper. It is found that radio sources
with small linear sizes (<150 kpc) have lower ionisation states, higher
emission line fluxes and broader line widths than larger radio sources. The
emission line ratios of small radio sources are in agreement with theoretical
shock ionisation predictions and their velocity profiles are distorted.
Together with the other emission line properties this indicates that shocks
associated with the radio source dominate the kinematics and ionisation of the
emission line gas during the period that the radio source is expanding through
the ISM. Gas clouds are accelerated by the shocks, giving rise to the irregular
velocity structures observed, whilst shock compression of the clouds and the
presence of the ionising photons associated with the shocks combine to lower
the ionisation state of the emission line gas. By contrast, in larger sources
the shock fronts have passed well beyond the emission line regions; their
emission line gas has much more settled kinematical properties, indicative of
rotation, and emission line ratios consistent with the dominant source of
ionising photons being the active galactic nucleus. (Abridged)
