CAP 804: Section 1 Part E Page 14
Pilot undergoing any form of flight test with a EASA or CAA
Authorised Examiner (other than case K)
PICUS for successful Test P/UT for unsuccessful test (including partial pass
Enter time in ‘P1’ column and have it certified by aircraft commander. Enter time in ‘Dual’ colum
So you must get the examiner's signature to be able to log it as PIC. Also the examiners name still goes in the PIC column.
No signature - no PIC - CAA do pick this up if you are using it towards CPL issue requirements.
In terms of Part FCL - 050 is the section but is open - and the AMC doesn't cover it - so it's up to the individual authorities as to what they accept.