I'm not an AME, but AIUI a 9/15 pass on a LAPL medical allows you to add a night rating to a LAPL. Since higher level licences (CPL PPL) have lower licence privileges embedded in them, it should theoretically be possible for a PPL/CPL to fly at night using their embedded LAPL privilages if they have a LAPL medical and 9/15 pass.
However, are you allowed to have more than one medical certificate, or would you need to give up your class 1 or 2 certificate in order to get night privileges?
This crazy situation just shows how stupid the current system is.