It's not clear why the organisers were unable to use the UCLOccupation account during the protest; perhaps it coincided with part of Twitter's network being down. The other alternative is that the internet surveillance powers Britain's authorities have allow them to use deep-packet inspection to selectively suppress the traffic of troublemakers as to maintain order, and that the surveillance boxes installed on all internet trunks have facilities to take out Twitter posts in this fashion. That wouldn't explain the non-appearance of the #demo2010 hashtag, though, unless the government's black boxes were designed to suppress posts for everyone but the original poster.
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