I've booked an Avis car hire in the U.S. via BA. I'll need an additional driver who is not on the inbound flight with me, a friend I'm meeting up with at the airport. The BA website noted that an additional driver is a free benefit for me as a BAEC member (Silver, if that matters).

My question is, is this really the case and will I have trouble getting Avis to honor this benefit when I roll up to the rental counter? The BA call center told me it wouldn't be a problem, but the printable voucher I've got from MMB, while saying toward the bottom that the additional driver is free, doesn't actually note that I'm availing of that on this booking. My fear would be getting socked with an additional charge by an Avis counter employee who's not familiar with this benefit.