GID44 - Logging of Flight Time (Acrobat Reader Required) is the document that Irv is talking about. He's quite right - apart from during your skills test you must have been either P1 or Pu/t, and that's something for you to agree with your instructor in advance.
FWIW, I was told (by an examiner) that the CAA just count any extra time logged P1s as P.u/t, but I'm not sure if that is true or not.