Submillimetre galaxies (SMGs) are among the most luminous dusty galaxies in the Universe, but their true nature remains unclear; are SMGs the progenitors of the massive elliptical galaxies we see in the local Universe, or are they just a short-lived phase among more typical star-forming galaxies? To explore this problem further, we investigate the clustering of 914 SMGs identified in the coincident area of the SCUBA-2 Cosmology Legacy Survey and the UKIDSS Ultra Deep Survey (UDS). Using angular cross-correlation techniques, we estimate the halo masses for the largest sample of SMGs to date and compare them with passive and star-forming galaxies selected in the same field. I demonstrate that SMGs, on average, occupy high-mass (M > 10^13 M_solar) dark matter halos at redshifts z > 2.5, consistent with being the progenitors of massive quiescent galaxies in present-day galaxy clusters. I will also show evidence of downsizing, in which SMG activity shifts to lower mass halos at lower redshifts. In terms of their clustering and halo masses, SMGs appear to be consistent with other star-forming galaxies at a given redshift.