FYI, like everything at Heathrow, T5 belongs entirely to BAA who rent the facilities to British Airways.
The staff at the front reception desks and "Guest Services" desks are British Airways' own staff. The brown uniformed catering staff are employed by Restaurant Associates (part of Compass Group).
BA staff are not permitted to help themselves to anything other than water from the lounges, despite the fact that our excessive price hike last year in the staff canteens run by Restaurant Associates goes to subsidise the free food in the T5 lounges. (Rather a sore point............)
British Airways' customers and entitled Executive Club cardholders are obviously self-financing. British Airways is entitled to charge One World airlines for each customer swiped into the entry system and this is partly the reason why we fastidiously stick to the "one guest" rule no matter how much our beloved Aadvantage Platinums stamp their feet! Whether BA applies the charge, or whether there are "contra" deals in place, I have no idea (but rather suspect there are).
Restaurant Associates' staff are not very well paid and I believe the odd bit of food and the read of a newspaper are little "perks" which, even if unofficial, I would not begrudge. Theirs is not the best job in the world, after all!