Flying Vueling to BCN today on a very expensive one way ticket booked as an Iberia codeshare. Managed to get into the First lounge, but after reading here, it seems I was just lucky. I was told that I couldn't bring a guest, but the agent let me in, so very grateful. I agree that if they're showing the Vueling flights in the lounge and you're BA gold, they should let you in. Just seems like an easy way to build goodwill and continued loyalty to BA/IAG.