I reported on this earlier, with photos. An article in today’s Guardian reports on research by Dr. Geoff Parnell that finds no trace of ravens at the Tower before the late 19th century, and also finds there were no ravens left in the Second World War, and yet the monarchy and the Tower did not come to an end.
bq. The earliest reference he found was 1895, in a piece in the RSPCA journal, The Animal World. One Edith Hawthorn referred to the tower’s pet cat being tormented by the ravens, Jenny and a nameless mate.
I can confirm that there was a cat at the Tower in June 2004, though probably not the same one.