Complex sentence: Since the year 2000, "choice based letting" (CBL) has been introduced to help ensure social housing was occupied speedily as tenants moved, but this can still favour the local over the non-local prospective tenant.
Split into simpler sentences: Since the year 2000, "choice-based lettings" (CBL) have been introduced to help ensure social housing was occupied speedily as tenants moved. This can still favour the local over the non-local prospective tenant.