UPDATE: We are watching a massive "cloud" of geo-tagged tweets moving from Embankment and Westminster and starting to work their way towards Hyde Park. We are also seeing what looks like a cloud of people coming towards Hyde Park from an alternative route in the north, though in London it is hard to make out flows of tweets on the ground, since the background nose of regular tweeting is so intense.
Using our HD tool we are seeing the highest level of tweeting coming from such a small concentration of people ever right now.
Using our Clima High Density Twitter analysis beta we can make out a large group of people coming out of Embankment London who we assume are getting ready for today's anti-government protest. This tool is very sensitive to very high levels of tweeting, giving a more precise picture of dense tweeting in a small space.
The tweet hastage #26march is exploding. If each tweet represents 1 person marching there would probably be several hundred thousands of protesters.