significance [@Lancaster2007]. We present the first in a series of papers discussing an X–ray selected sample of 33 clusters with well understood selection effects. This paper contains details of our OCRA–p observations of a statistically complete subsample of 18 clusters. The structure of the paper is as follows. In Section 2 we give a brief description of the Toruń 32-m telescope and the OCRA-p receiver. Section 3 contains details of the cluster sample. The observations and data reduction are described in Section 4, and the problem of radio source contamination is detailed in Section 5. Section 6 gives a brief overview of our X-ray analysis, and Section 7 presents our results. We discuss these results and conclude in Section 8. Throughout the paper we adopt the following cosmological parameter values: $H_0 = 70 \, \mathrm{km} \, \mathrm{s}^{-1} \,
\mathrm{Mpc}^{-1}$, $\Omega_{\mathrm{m}0} = 0.3$, $\Omega_{\Lambda 0}
= 0.7$.

THE TORUN TELESCOPE AND OCRA-p
==============================

The Toruń observatory is located in Piwnice, 15km outside Toruń in northern Poland. The telescope consists of a 32-m parabolic dish and 3.2-m sub-reflector, with a fully steerable classical Alt–Az mount. It has receivers operating at 1.4-1.7, 5, 6.8, 12 and 30GHz. The telescope is used for a 