I'm about to get in contact with Twitter the second I've posted this. I'm more than a little furious; after all, all the URLs that link to it are now incorrect, all the lifts, all the (puppet-mastered) banter is gone. Cool URLs don't change, and these have just gone. And in their place: marketing.Where's @towerbridge?
I've never pretended to be an official account; I've never dissimulated; no-one from the exhibition has ever got in touch with me about the bot.
So, for the time being: this is why the bot has disappeared. I'm very, very cross, and perhaps a little upset; the robots are our friends, after all.