Originally Posted by NorthSouth
It only needs one of the two to be on a procedural service for separation to be applied. If the outbound chooses to be on a BS (presumably in order to avoid delays) but there's an inbound on a PS, the outbound will get no benefit because the controler will be applying vertical and/or time/distance separations to keep them clear of the inbound.
If one is on a procedural and the other on the basic there is nothing to stop the controller launching the basic as there is no requirement to provide separation between procedural and basic aircraft
Only between participating procedural aircraft
If a likelyhood of confliction exists then the controller may pass traffic info
Feels kind of strange though