Join Date: Oct 2006
Location: London, UK
Programs: BA Gold, VS Silver, SQ Silver, IHG Plat Amb, Hilton Gold, Marriott Plat, Accor Silver, Radisson Prem
Posts: 16,873
Yes, yourself and your guest need to be travelling on a oneworld airline to get access to a oneworld lounge or a third party lounge operated on behalf of a oneworld airline.
As a BA Gold, you (but no guest) can access any BA operated Executive Club/Terraces/Galleries Club lounge travelling on any airline, where your flight departs from the same terminal as where the BA lounge is located.