I can answer my own question. Admittedly we played a bit dumb. We had obviously booked the flight before BA withdrew from the lounge as it was mentioned our booking confirmation. We showed this to the lady at check-in who was confused but telephoned a colleague who confirmed that BA had withdrawn their association with the lounge. We asked about a voucher but the answer was no. We did get to use fast track security which is called something like the green route and that was very efficient. No sticker was needed which is fortunate as are on HBO using the boarding passes on our phones. We are now in the lounge, courtesy of Priority Pass waiting for our flight whose delay is getting longer as I type.