for the details of the CMB work). The next phase of the project is an 8–element array, OCRA–Faraday ([@Peel2009]), which was mounted on the telescope in late 2009. This is still in the commissioning phase but is expected to be fully operational in autumn 2011, and can be upgraded to 16 elements in the future.

THE CLUSTER SAMPLE {#sec:clusters}
==================

In order to derive meaningful cosmological results, or indeed to comment on universal cluster properties, it is necessary to use a ‘fair’ sample, or at least one where the selection biases are clear and well understood. Large samples fulfilling these criteria are rare in SZ astronomy, largely due to the various practical challenges which observers must overcome. In this work, we attempt to select and observe such a sample, and turn to the ROSAT All–Sky Survey in the first instance.

The Brightest Cluster Sample (BCS, [@Ebeling1998]) is derived from a careful analysis of the ROSAT All-Sky Survey (RASS, [@Voges1999]) data at $\delta > 0^{\circ}$. The resulting catalogue is 90% flux complete to a limit of $f_{\mathrm{X}} = 4.4
\times 10^{-12}$ergcm$^{-2}$s$^{-1}$ in the 0.1-2.4keV energy band. Since the SZ surface brightness of a cluster is essentially unaffected by redshift, we select 