Thanks Ksmax dor your articulate comments, that was my experience Sunday as well. But get ready for people who werent even there to give you a very British brush back and suggest you should be thankful for the letter (how polite, no?), that there was no reason to extend the hours of the lounges or airport counters (because, all the friendly staff you could try to reach by phone!) and just generally what else could BA have done? The airport AND the airline experienced complete system failures on Sunday.
BTW, every FTer flying thru T5 Heathrow should learn this trick——-> YOU CAN ACCESS IMMIGRATION BY TAKING THE TRAIN TO T5C AND THEN JUST STAYING ON WHEN IT GOES BACK TO T5A. Once the lounge closure was announced, i used this trick to access fast track immigration and be on the HEx in 20 minutes.