After trying to sorta understand what you're going on about and failing miserably, I'll put in a little which might actually mean less than nowt, but here goes.
If you are IFR in class G airspace, we have no requirements to separate. Under a RIS/RAS we will aid by giving traffic info, and under a RIS, further this by saying 'if unseen turn/change level....'
In class F, we separate IFR's that are known to us, VFR as above.
In classes D+E, IFR's separated, and traffic info given to IFR's on VFR's, and vv in D.
In class C, separate IFR's from everything, VFR's get traffic on VFR's.
Class B, separate everything, but how you can be VFR in UK Class B is another matter!!
Class A, VFR not permitted.
Basically, outside you have to be under a RIS/RAS to get any help as IFR, but we can refuse to give this due workload, and can limit it taking away responsibilty again due workload, or a large number of unknown returns, or due to you being on the edge of the radar cover or limits.
Must go, coffee time
