JimL - thanks a for clear, concise reply - I am enlightened.
Decks , I don't know about Ireland but I suspect that the UK civvy SAR (of which Portland is day only) fly in accordance with all the sub paras and sub, sub, paras mentioned by others and are in fact flying IFR below 3000' in sight of the surface. UK mil SAR does fly VFR at night either reversionary (no NVG) or with NVG. I believe the Bristows SAR guys have been given clearance by the CAA to fly with goggles but I heard that 3rd or 4th hand.
Sasless - I hope the UK HEMS do get to fly at night but that the same mistakes you have highlighted on other threads about US EMS safety are not repeated; maybe they will go down the twin pilot/twin engine/IFR/NVG route rather than cutting costs and safety.