Sorry I've not had time to come back in on this since I started it...
My experience at Oxford certainly was that ATC would enquire when I was inbound whether I was VFR or IFR. If I was solo I would say IFR (so I didn't need an observer) and they would separate me; if I had someone with me I would say VFR and they would explicitly state that I was responsible for my own separation. In fact as Oxford is in class G I was responsible for my own separation (see and avoid) in either case in VMC, but at least it made it clear. I'm now operating out of Benson where they are happy to accept me for an ILS/PAR on request, if I'm inbound from somewhere else and either genuinely in need or they can fit me it (e.g. I did an ILS when the viz was 4500m - not legally required but definitely made me feel happier!)
Chilli: don't forget that plain-vanilla JAR PPLs can fly IFR in this country in VMC. I can't see anything legally preventing them requesting an instrument approach in VMC, therefore, though I don't think any would in fact. NPPLs are of course day VFR only.
Tim