VMC is not the same as VFR.
A difficult issue this, that regularly gives me professional headaches.
To fly IFR outside of controlled airspace means flying in accordance with rules 29 and 30. If a pilot is required to maintain VMC, they can still do so.
To fly VMC, you need to maintain the legal minima required for your particular combination of aeroplane, speed and licence - that doesn't stop you flying VFR OR IFR.
But, here's the thorny bit - and UK-CAA probably hold most of the blame for this. Certain aeroplanes are required by law to maintain VFR (not VMC, VFR). All permit aeroplanes fall into this category.
So, if I go flying in a permit aeroplane, I must remain VFR - the permit conditions say so. But, if I choose to comply with rules 29 and 30 (a very sensible thing to do, particularly on a long run at altitude), then I am by definition flying IFR - notwithstanding that I am outside of controlled airspace, have not filed an IFR flightplan, and may not even be in RT communication with anybody.
At this point, I'm going for a lie down in a darkened room, in night IFR.
G