everything John has said is true.
It was common practice for P&O officers to "wheel-in" female passengers, especially the younger and more attractive ones. Such liaisons, which often lasted for an entire voyage, were not 'legal' but were tolerated. It was also much easy for officers than ratings to form such liaisons.
Engineer officers outnumbered the officers in the other departments (Deck and Pursers) and their accommodation was conveniently situated close to that of passengers, so wheeling in was easier for them than for Deck officers who were quartered in close proximity to the ship's bridge. Also, engineers were notorious for their amorous adventures.
I noted that you had also posted a message on Seadogs-Reunited. I believe that the website contains lists of officers, by ship, who were at sea in 1965.
Not sure if this helps you in any way.