I think you'll find the PoH is also owned by a seperate company.
Nathan, without wishing to contradict you, I am interested to know what source you are quoting for Dover based ships, as that is not my understanding. I understand that only the Dover/Calais 'Chunnel Beaters' were purchased outright (and possibly since subject to a sell/leaseback deal...
No, to say that if PO owned both outright that it would automatically mean both were British crews, is not correct. The country of registration, country of (nominal ownership) do not need to be the same as the (non senior) crew.