One of them is when an instrument rated pilot practice IFR (to gain IFR currency), he/she wears a IFR hood and simulates IFR condition while the other safty pilot provides look-out. In this case, they can both log P1 (not sure which type of P1 though).
again people are mixing up CAA (JAA) and FAA rules. This question is about the CAA and JAA as far as I understand it.
Yes in the USA system you can both log PIC when doing instrument training (but note the requirements....).
No in JAALand you cannot. End of story. In fact in the UK you do not even need a PPL in the RHS as safety pilot, whereas in the USA you MUST have a licenced and rated safety pilot.