How are people getting confused by this? It should be explained on day one.
Every single pilot aircraft has to have a P1/PIC (it's the same thing) and under EASA it's simple:
If you're on your own then it's you.
If you're carrying passengers it's still you.
If you're receiving instruction then it's the FI
If there's an FI sat next to you, then you're P/UT