I purchased a full fare ticket at the airport from Edinburgh to LHR and walked up to the lounge. Even though the ticket was full fare, it didn't have 'Business UK printed on it'. The dude at the door was a bit of a weapon, so I let him give me the speech about not being able to use the lounge and let him 'shame me' in the way only these people know how to; 'sorry about that' etc etc
Once a suitable amount of time had gone by, I put my BAEC card down in front of him and let him apologise for 10 minutes before finally correcting him and saying he should have let me in anyway.
Edit: The point I'm making here is most of you know the access rules much better than they do.