There have been two disturbing cases in recent years of counter-terrorism powers being used to clamp down on peaceful and legitimate protests.
In March 2003 the police stopped several coachloads of protesters from travelling to the US airbase at Fairford in Oxfordshire, citing anti-terrorism powers as their justification.
At the September 2003 protests against DSEI arms fair in east London there were 144 arrests, at least two of them under the Terrorism Act 2000.
Police are planning to impose an exclusion zone around ExCeL centre for DSEI 2005, which takes place on 13-16 September. This will prevent any kind of effective protest there.