We present radio continuum and polarization maps of four ‘classical double’ radio galaxies, overlaid on optical emission-line images. The sources (3C 247, 263.1, 280 and 299) are all small, powerful and distant (with $D \lt 200 \,\text kpc, {P}_{178} \gt {10}^{26.8}\,\text {W}\,\text {Hz}^{-1} \text {sr}^{-1},0.37 \lt z \lt 1.0$). In three cases we find that the emission-line gas lies on that side of the radio source for which the depolarization is stronger, the hotspot closer to the core and the radio spectrum steeper. We discuss the origin of these features, and suggest that a non-symmetrical distribution of gas around the host galaxy could account for the observed asymmetries.