Agree with Workisfun's comments... would add (although don't have a copy of JSP552 to hand so not verbatim)
High traffic density is not an excuse not to offer avoiding action or call traffic.
that when operating in high density/high workload the Controller will give priority to separation from known traffic... i.e. separation from unknown traffic may not be applied, but in these circumstances the Controller is to ATTEMPT to pass traffic information on the unkown traffic... attempt, note!
Why offer RAS?... because you asked for it. Normally the service requested is the one provided... as pointed out by my colleagues, a Controller is entitled to downgrade service due to workload, but "high traffic density" does not necessarily equal "high workload". It just may be a lot of aircraft in one area when achieving standard separation is unlikely NO MATTER how busy the Controller is.