Hello Merak
I have more than 1600 hours on the BE20, flying for a South African operator on contract in Africa. I understand the CAA require 2 pilots for all aircraft operating under IFR and configured to carry more than 9 pax.
We always flew under IFR and carried 10 pax... in addition our client (UN) required 2-crew operation. Initially I only had a P2 rating so had to log it all as P2. Once I got the P1 rating, I logged P1 leg-for-leg, whenever I was the flying pilot. (in practice I split the total time for each day, half P1 and half P2).
So I have more than 400 hours logged as P1 on the BE20, even though I was never actually a captain. The SA CAA were happy to accept this when they issued me with my ATPL, counting ALL of the Dual time, ALL of the P1 time, and HALF of the P2 time.
Out of interest - in the UK this would be called PICUS - "Pilot in command under supervision". Can by logged by a co-pilot whenever he's pilot flying, and those hours can be used for a higher license or promotion where P1 time is needed.
The UK CAA also happily accepted the hours when they issued my JAA ATPL but they did require a letter from the operator stating that our operation was a proper 2-crew one.
Hope this helps
JD