I've seen it happen many times, it's nothing new. Sometimes it appears to be a college or partner of someone travelling in the higher class, sometimes it appears to be staff or crew or perhaps just friends of crew. It makes me jealous, but that just because I wish it was me getting the invite ;-) . But as in most walks of life, if you are staff in a company or know someone that can pull strings there are often perks to be had. I'm sure most of us given the chance to take advantage of any such perks would not hesitate to do so. Provided it doesn't negatively impact anyone else, I don't really see it as something to be concerned about. Who knows, maybe one day the OP will become a close friend of a BA staff member, would he then decline any discreet invites to a nicer seat?