The government's controversial Terrorism Act comes into force today, outlawing the glorification of terrorism and paving the way for the detention of terror suspects for 28 days without charge.
The bill, introduced in response to the July 7 bombings, was opposed by both the Conservatives and Liberal Democrats, and saw Tony Blair's first Commons defeat since coming to power, when Labour rebels overturned a government clause allowing 90 days detention.
The act creates new offences of undertaking terrorism training, preparation of or planning a terrorist act and disseminating terrorist publications.
But the most contentious measures were the detention period without trial for suspects - finally increased from 14 days to 28 days as a compromise - and the new offence of glorification, which the House of Lords rejected five time before finally voting it through last month.
Legal experts warned that "glorification" was too widely drawn, and could encompass opposition to totalitarian regimes worldwide, while some politicians and civil liberties campaigners claimed that such actions were already banned.
Although the Home Office said a new terrorism bill was already being planned before the July 7 attacks, the bombing gave the bill added impetus.
The prime minister outlined a series of proposals last summer, and the opposition home affairs spokesman and party leaders were invited to Downing Street to discuss the measures.
Although the act comes into force today, the measure to detain terror suspects for up to 28 days rather than the existing 14 will come into force later, following consultation with police chief constables.
Any detention longer than 48 hours requires judicial oversight.
The act makes nuclear sites into designated areas where trespass can become a terrorist offence.
Liberty spokesman Doug Jewell said the act's provisions were too broad.
"The problem with this is that the encouragement and glorification laws which are coming in today are so broad that anyone supporting violence to remove a regime anywhere in the world now or in the past would theoretically get caught up," he said.
The shadow home secretary, David Davis, said: "We welcome much of what is in this act but have concerns about the glorification of terror offence.
"During the passage of the bill we secured an assurance from the government that this would be revisited when the home secretary consolidates the terror laws.
"It is important to remember, however, that the fight against terror is not simply about introducing new laws, but also having the will to use them.
"Abu Hamza was eventually convicted but it was under legislation that pre-dated 9/11 - in fact six of his convictions were under legislation dating back to 1861."
Labour MP Jeremy Corbyn - one of the leading rebels against the terror laws - branded the glorification ban "absurd".
"The legislation is misguided and the whole concept of glorification is frankly absurd and will end up entrapping the innocent and preventing legitimate debate.
"What some would call a freedom fight going on in another country others might term a terrorist offence.
"Nelson Mandela was branded a terrorist by Margaret Thatcher; he was later branded a freedom fighter," he said.