Hi, in terms of the British library situation, I feel that this is the norm . Most PRS registered libraries in the U.K. the ones who are related to MCPs.that is publishing etc want to sign you as a composer for specific tracks . They usually want an album . This often means an album on a particular theme.eg, Jazz, World , sport ,orchestral , piano etc … choose your own examples..! Most of the decent libraries have access into the BBC sound mouse which gives access to a music editor to view suitable and appropriate tracks and download them to try with a specific film / documentary, scene etc . I feel if you want to progress you need to find a library that has access to these companies. Whatever you do , the production needs to be good and a bit different… I only speak from experience. Good luck … Phil