Just going back to the night time question, in the UK and outside controlled airspace, Rules 29 and 30 apply. If you distill these rules down, they say if you fly below 3000 ft, stay clear of cloud and in sight of the surface, then you are complying with the IFR. And that's how lots of flights are conducted visually at night in the UK.
To be fair, it gets a bit more complex inside controlled airspace - but mainly for the controller!