The CAA have always been clear that for a flight to be an "Instructional Flight"
(ie One person logging PIC and teaching a second person who logs PUT) then
the Instructor must have instructional privileges for all aspects of the flight.
That was true under National rules especially with regard to teaching for the IR at night but, its no longer the CAA's call. It's down to what is written in Part FCL.
I don't think there is any debate regarding a CRI not being able to train for a Night Rating however; there is nothing to prohibit Class rating training including refresher training being conducted at any time of the day so long as both pilots are appropriately rated e.g night rating at Night. If you go back to the old UK LPC/LST forms it actually included a column for night circuits (if required).