Crab,
I'm not sure if I missed your point but to fly IFR at night a helicopter flying below 3000ft with regard to visibility only has to obey IFR Rule 29(d):
29 Without prejudice to the provisions of rule 5, in order to comply with the Instrument Flight Rules an aircraft shall not fly at a height of less than 1000 feet above the highest obstacle within a distance of 5 nautical miles of the aircraft unless:
(a) it is necessary for the aircraft to do so in order to take off or land;
(b) the aircraft is flying on a route notified for the purposes of this rule;
(c) the aircraft has been otherwise authorised by the competent authority; or
(d) the aircraft is flying at an altitude not exceeding 3000 feet above mean sea level and remains clear of cloud and in sight of the surface.
This is the CAAs way of making NVFR the defacto standard. However, the helicopter does have to be crewed and equipped in accordance with schedule 4 and 5.