It says here,
"A pilot flying as 'pilot-in-command under supervision' shall enter flight time acquired in this manner in the 'Pilot-in-command (P1)' column and 'P1(u/s)' in the 'Holders Operating Capacity' column. In each instance the Commander of the aircraft must certify the entry."
This log-book was printed before JAA.
It makes no mention of the licence held but this should not be relevant. To be able to put just 'P1' in the 'Holders Operating Capacity' column you will need to be the nominated Commander of the aircraft by your company, in other words you will hold a command with that company. If this is the case you can put your name in the 'Commander' column, otherwise it should be the commander nominated by the company for that flight.
Suggest you check this out with the CAA as you are likely to get a dozen different answers here on PPRuNe!!!
