hempy, thanks for the confirmation that BOAC was entirely at the government's disposal 1940-45. Hence I see no reason why anyone traveling officially did not warrant some consideration to travel with them. The consideration would not have been their social status, even be they (God forbid!) NCO aircrew. The consideration would have been the urgency of their duties and whether there was room for them.
I imagine most of the time the answer to the latter would have been 'no', hence the perceived rarity of such an experience. As pointed out though, those in the know would probably have fared better than those that were not. I would guess therefore that ferry pilots, and those that administered their comings and goings, fared better than most.
I see that BOAC administered the ATA, for example, despite control moving from the RAF to the Ministry of Aircraft Production.