So it looks like I went to the lunch because it was free but couldn't actually be arsed to attend the lecture afterwards. I need to find the lecturer's email address & apologise.
Also, I went back to the Graduate Office in my department at Birkbeck (= rather small College of the University of London) to complain, & they were shocked that UCL (= large & prestigious College of the U o L) had rooms which weren't accessible! Dudes... Did you think to ask?
Though I found out that the Graduate Symposium isn't in Mill Hill at all, it's in UCL. This would be good, if not for the fact it's currently booked to be in the same venue that I couldn't get into today. Laugh? It's that or cry.