The number of rich clusters of galaxies beyond redshift z=1.0 is a strong function of the density of the Universe. In high-omega models very few clusters are expected beyond z=0.8 whereas low-omega models predict many per square degree. The UKIDSS LAS offers a unique opportunity to select clusters in the crucial z=0.5-1.5 range through detection of galaxy overdensities. For a limit of K=18.4, we predict at least 1,000 rich clusters (>1014M(sun)) between z=0.5-1.0 and 100 with z=1.0-1.5 for an omegam=0.3, lambda=0.7 Universe (Gillbank & Bower, in preparation). With multi-colour photometry it is possible to suppress the z<1 galaxy foreground and detect lower mass clusters, bringing the number of detected cluster up to 6,000 and 1,000 in z=0.5-1.0 and z=1.0-1.5 respectively.
This sample of rich clusters will complement the samples coming from the deeper, but narrower field DXS and UDS surveys. The LAS-based sample will be especially useful to trace the large scale structure on the largest scales at z>1 and reliably measure the cluster-cluster correlation function for the most massive collapsed systems at this epoch. In addition it will provide a unique laboratory for galaxy evolution studies, extending the baseline for tracing the evolution of galaxies in high density environments across 75% of the Hubble time, back to z~1.5.