on luminosity, imposing a limit of $L_{\mathrm{X}} \geqslant 13.08\times10^{44}\mathrm{erg\,s^{-1}}$ (the luminosity of A773 in the BCS catalogue). In addition, we impose the criterion $z>0.2$ due to the $3'.1$ beam–throw of OCRA; observations at lower redshift are inefficient with this instrument. Our basic sample then consists of 18 clusters. We do not reject any clusters based on their radio–source environments at this stage, even though we appreciate the difficulties which this policy may introduce. This has the advantage of allowing us to investigate any correlation between gas properties and those of a central radio galaxy.

We reject one cluster from the basic 18–cluster sample, A689, as on further investigation we have found that the ROSAT data are contaminated by a bright central point source (Giles et al., in preparation). After removing this source from the *Chandra* data, the luminosity is just $(1.66\pm0.24)\times10^{44} \mathrm{erg
 \,s}^{-1}$, more than a factor 8 below the limiting luminosity of the cluster sample. The sample is summarised in Table \[tab:coord\]. These clusters appear not to be exceptional in their X–ray structures, and, indeed, follow the expected X-ray scaling relations (see Section \[sec:Xscale\]).

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  Cluster                RA             Dec        $\Delta$RA   $\Delta$Dec    $z$         $L_\mathrm{x}$
                       (J2000)        