I had emailed Athenaeum to book the afternoon tea for 21st March, to my delight they had availability on that date when I had emailed them, so I replied that I would see them there! Taking it as no news is good news. I turned up for the afternoon tea, only to be told that I did not have reservation and that they were fully booked, even though it was completely empty and there was a slot on their reservation sheet clearly visible. I was extremely disappointed that no member of staff contacted me by email or telephone (my number was in the email), especially as it was my birthday.
Top tip: Do not book through Athenaeum itself.