Actually since JAR it is a Night Qualification not a Night rating. To remove the restriction an instructor must attend a course with an FIC instructor of at least TWO hours ground school then a flight of at least one hour to demonstrate ability to teach ex 12/13 (circuits) at night. Also according to the latest Trainingcom the instructor should undertake sufficient night navigation training. The restriction is removed by the FIC instructor signing off the relevant form before presenting it to CAA for the removal from the licence, but remember if you are still a FI(R) you cannot send first solos at night, either circuits or nav.