Sticking my neck out here but........
I think a lot of pilots are under a misapprehension here regards the fact that to a controller as far as separation goes it doesn't always matter what flight rules you are under (In the UK). The main thing is what service you are provided, and the airspace you are within, that defines what separation you are given. So just assuming because you are IFR you will be given separation is a no no, as is I'm VFR and the controller is responsible for terrain separation in class D Airspace because it is a radar control service (from a pilot with a lot of hours flying a scheduled service VFR in the daytime I kid you not).
So it's not eas,y and i'm sure I will get told that I've got this all wrong, and I'm sure I have as I haven't had to worry about this for a few years now Thank the Lord.
TS