Originally Posted by m8_rotate

This seems an extreme reason to access the lounges at T3. However, it could be done, but, and this is a big but, you would have to be offloaded from the aircraft, for you to access the arrivals area. This means that you would have to come up with a good reason to be offloaded and let the BA lounge staff know. You would then be guided to arrivals. There is a door that has to be activated, so you can do this, and it is manned. It seems a very complicated and risky way of accessing the lounges, but, technically, I believe it is possible.