Same ticket (to BA to LHR) was v easy. went to transfer desk, waited until all pax had arrived (about 8-10 of us) then wandered through scanning security again and to lounge. Was in lounge <45 mins post wheels down. Didnt need to clear immigration. Oddly (!) was asked for codes to suitcase in case the authorities needed to check. Declined and said they had TSA lock. This added a ten min delay whilst she spoke into a telephone.....