I was in 3A flying LHR-LAX. I remember just before departure 3 diplomats from the Middle East boarded last from a limo. We did a slow turn just over Greenland and I remember the maps and phones being turned off. About 30 minutes later the captain said "Due to an international security incident Unite States airspace has been closed and we are waiting to be told where to go". A few hours later we arrived in Cardiff where the diplomats were met by a police car and the rest of us told we would be coached to a hotel and fly the next day. I didn't believe this would happen so shared a taxi with 2 others I got talking to all the way back to Reading.
I got a call on the Thursday evening from BA saying they could fly me out the following day which I did and that was a very odd experience.