  We present a submillimetre survey of seven high-z galaxy clusters
(0.64<z<1.0) using the Submillimetre Common-User Bolometer Array (SCUBA) at 850
and 450 um. The targets, of similar richness and redshift, are selected from
the Red-sequence Cluster Survey (RCS). We use this sample to investigate the
apparent excess of submillimetre source counts in the direction of cluster
fields compared to blank fields. The sample consists of three galaxy clusters
that exhibit multiple optical arcs due to strong gravitational lensing, and a
control group of four clusters with no apparent strong lensing. A tentative
excess of 2.7-sigma is seen in the number density of submillimetre luminous
galaxies (SMGs) within the lensing cluster fields compared to that in the
control group. Ancillary observations at radio, mid-infrared, optical, and
X-ray wavelengths allow for the identification of counterparts to many of the
SMGs. Utilizing photometric redshifts, we conclude that at least three of the
galaxies within the lensing fields have redshifts consistent with the clusters
and implied infrared luminosities of ~10^12 Lsol. The existence of SMG cluster
members may therefore be boosting source counts in the lensing cluster fields,
which might be an effect of the dynamical state of those clusters. However, we
find that the removal of potential cluster members from the counts analysis
does not entirely eliminate the difference between the cluster samples. We also
investigate possible occurrences of lensing between background SMGs and lower-z
optical galaxies, though further observations are required to make any
conclusive claims. Although the excess counts between the two cluster samples
have not been unambiguously accounted for, these results warrant caution for
interpreting submillimetre source counts in cluster fields and point source
contamination for Sunyaev-Zel'dovich surveys. [Abridged]
