My understanding (from the pilot side) of the rules for night flight in the UK are
It is IFR, except it can be SVRF in a Control Zone.
However, my understanding of IFR also is that in Class G airspace (and logically in an ATZ in class G)
IFR is -
quadrantals above 3000 ft
1000 ft above highest obstacle within 5 miles (or on a notified route/procedure/etc.)
The 1000 ft restriction is removed when at less than 3000 ft MSL and clear of clouds in sight of the surface.
Therefore, doing circuits (day or night) could be in compliance with IFR and there would be no observable difference to VFR circuits.