I have to admit, the first few times I used the F lounge at LHR, I actually thought I'd been directed to the Business section and that the F lounge was off-limits to me as a Qantas Emerald. I think I just assumed only BA Gold's got to go into the F part when not flying F.
Back then I also didn't realise I was allowed to use F Wing security and always went the long way around!! Then one day I read a post on this forum saying F Wing was open to all OW Emerald and my LHR T5 experience has been forever improved. It was only then I realised I had actually been going into the F lounge all along!