I head for the US embassy in Grosvenor Square, where the Stop the War Coalition is holding its own grim demonstration. This is a very different phenomenon: there is no fancy-dress and only one or two home-made signs among the hundreds mass-produced and handed out by StW and its partners. A large proportion of these placards bear the logo of one of these partners, the British Muslim Initiative, whose president, Mohammed Sawalha, was exposed by BBC's Panorama in 2006 as a major Hamas activist and fundraiser in the early nineties. In February, Sawalha was one of 90 signatories to the Istanbul Statement, a jihadist edict that had nothing to do with peace and everything to do with the dire dream of a total Hamas victory.

Although Daud Abdullah, another British signatory to the Istanbul Statement, will later take to the stage in Trafalgar Square to address this crowd, there's no one quite like that at the embassy - the useful idiots are handling everything all by themselves. This is no great task, because apart from a couple of people selling Marxist literature, there's only one thing happening: a pair of adolescent boys are bouncing up and down, ginger hair in disarray, and taking turns on a megaphone. Four bars of "Occupation is a crime, free Iraq and Palestine", followed by four bars of "From the river to the sea, Palestine will be free", followed by four bars of "Israel you can't hide, we charge you with genocide", repeated for an hour with the crowd chanting along. On the grass away from the main crowd, near where four octogenarian members of "Quakers for Justice" are collapsed on a quilt beneath their banner, a woman mutters these axioms solemnly to herself, as if for her own personal consolation.

Back at the G20 Meltdown protest, the windows of the branch of the already nationalised Royal Bank of Scotland have been smashed and graffitied. Prominent among the slogans there, "Peado" [sic] best captures the haywire motivation for this attack. The tone for the rest of the day has now been set and the police are in full riot gear. A man taunts them over a megaphone: "Bankers are wankers. Smoke weed everyday. Gordon Brown and the Illuminati puppets are puppets. 9/11 and 7/7 were inside jobs. Gordon Brown planned 9/11." The ragged look in his eyes tells me that he has no idea whether he is joking or being serious.