Online says the dates we are in London are sold out. Can you still write for the tickets and receive them or they have they gone to online only?
Online only I believe. Booked mine in February for my November travel dates. 7 years ago it was snail mail and tix were plentiful. Now, with RS spreading the word and the Internet its no longer a hidden gem and more difficult to attend.
I would certainly at least try to get them (by writing)!
I attended the Ceremony of the Keys way back in '92, when writing 6 months in advance was the only option. It is so worth the effort!