OK, I was misreading the objection as being about using livery_hall. Agreed it's not an amenity, but what is it? I looked at two example livery halls, which were classified only as building=yes and building=office. And to my surprise, Mercers (Ironmonger Lane) doesn't even seem to be mapped. My best guess would be that they are trade associations, but I can't find that in the wiki.