In the morning this lounge functions as PP lounge; oneworld lounge access rules don't apply. In the afternoon, when it is open as a BA lounge it often refuses entry to those not flying BA (especially those flying domestic) due to space limitations (PHL is also another lounge that regularly refuses entry). See:
https://www.flyertalk.com/forum/brit...-lounge-6.html
https://www.flyertalk.com/forum/brit...ry-phl-16.html