I've always found logging hours quite simple here in the UK. Any dual time with an instructor is logged P u/t, unless like whirly say's, he/she allows you to log P1 (in effect they were a passenger). Someone has to log P1 so this is ok in my book. I occassionally fly with an instructor friend. If it's an instructional flight then it's P u/t, but if we're just flying together then we decide who's P1 (even an instructor can be a passenger). Flights with an examiner for a test which is passed are be logged as P1/S and any solo flight, or flights in command are P1. Only one person can log P1, so your role during flights with fellow PPL's have to be agreed between yourselves. P2 and other logging is usually for commercial crew unless the aircraft is required to have two pilots and you are actually P2 (not many that PPL's can fly spring to mind but I know there are a few).
P1 and PIC are the same thing.
SS