The two-tier system of local government introduced in 1975 lasted until 1 April 1996 when the Local Government etc. (Scotland) Act 1994 came into effect, abolishing the regions and districts and replacing them with 32 unitary authorities.
Every local authority was required to have a qualified chief social work officer, but many of these did not operate a senior executive level. Over time, social work departments tended to be replaced by combinations led by non-social work staff.
Source: Prof Bill Whyte, 03/04/17