Speaking for the first time since the appeal verdict on Friday, Mr Clay, 23, said: "People who are going about totally legitimate, lawful forms of protest and activity are being made to feel like criminals and recorded and monitored by the state for no reason.
The men were arrested and convicted in June 2008 of obstructing police officers or police photographers, and ordered to pay nearly £2,000 in fines.
At Inner London crown court, the prosecution claimed police feared people at the meeting were planning a violent protest against US president George W Bush, who was visiting London. But defence lawyers argued the police had no supporting evidence and were harassing the activists.
Judge Robert Fraser said: "We emphasise we do not say the police did not have a legitimate aim, but the Crown failed to satisfy us to the relevant standard."
A Scotland Yard spokesman said: "Fit teams are something that have been around for a long while and are an overt tactic at high-profile demonstrations and events. They are there so that if people get out of hand then the evidence has already been gathered."
