pilotincommand; could you please post the regulations in regard to that?
If it is indeed the case then the CAA (who added the rating without issue), TRTO (who taught the type rating course without issue), pilot and operator concerned are all mistaken.
LASORS, Section A, Appendix F, CPL (Paragraph 7) states that a CPL may act as co-pilot on any aeroplane for which he is rated; is does not state a requirement that it be single-crew.
Since everything in aviation is permitted unless it is expressly prohibited, I would be interested to see information to the contrary.