International terrorism is posing Britain its most sustained threat since the end of World War Two and can only be tackled with the public's help, Home Secretary John Reid said on Wednesday. In a speech to the think tank Demos in London, Reid said there was "not one inch of room for complacency" over security. "We are probably in the most sustained period of severe threat since the end of World War Two," he said in excerpts released by the Home Office. "Since 7/7, at least 4 terrorist plots have been successfully disrupted by security services. That is the ones that we know of. There are as (U.S Defence secretary) Donald Rumsfeld famously once said, not only known unknowns but the unknown unknowns. Yet in spite of these successes, we remain unable to adapt our institutions and our legal orthodoxy as fast as I believe we need to adapt", Reid said. "What happens when the threat to the nation , and hence to all of us, as a community represented by the state, in a particular sense, comes not from the tendencies of a fascist, totalitarian state, but from what might be called fascist individuals", he added. Reid's comments echo those regularly made in recent months by senior police officers and security officials. On the anniversary of the July 7 suicide bombings, London's police chief Ian Blair said the threat had "palpably increased" in the year following the attacks on the capital and that "further atrocities" were being planned. Blair and his senior colleagues have also repeatedly said they needed support and intelligence from Muslim communities if they are able to counter the threat from radical Islamists based in the UK and abroad. Reid's speech came a week after the Court of Appeal backed a ruling which threw out a key plank of the government's anti-terrorism powers when it agreed that "control orders" breached six suspects' human rights. The orders allowed police to place restrictions on terrorism suspects who had not been charged with a crime. Following the ruling, Reid said he would use less severe powers against the six men but vowed to appeal against the verdict. The decision was announced by the court on the same day the government unveiled a new security alert system which said Britain was at "severe" risk of a terrorist attack -- the second highest level of threat.