Britain's Home Office says more than half of those arrested on suspicion of terrorism since 2001 have been freed without being charged.
The government released figures on Wednesday to detail arrests and convictions under Britain's terrorism laws between September 2001 and March 2008.
Of 1,471 people arrested, 819 were freed by police.
About 7 percent - or 102 people - were convicted of an offense under Britain's terrorism laws. The ministry says 94 people were convicted of related offenses under other laws, like conspiracy to murder.
Police say that since 2001 more than a dozen terrorist plots have been attempted in Britain.
Attacks on London's transit system on July 7, 2005, killed 52 people and four suicide bombers.