DaveR, I think you maybe confusing Affordable Housing with shared ownership, shared equity and homebuy schemes which have all been around for many years and are not necessarily limited to local people.
Housing Associations tend to support shared ownership with a normal mortgage from a lender and top it up with funds allocated to them from the Welsh Government, which can act the same way a cash deposit does.
Schemes are usually dealt with on a first come, first served basis from a long waiting list with no points system involved.
However, a larger family usually gets the greater support.