Laws to restrict hate preaching must be tightened, the government has been told, after Anjem Choudary was found guilty of inviting support for ISIS.
It took counter terror police nearly 20 years to bring the 49-year-old to trial after he remained "just within the law" for most of their investigation. He was finally arrested in 2014 after he swore an oath of allegiance to ISIS.
Keith Vaz, chair of the influential home affairs select committee, called for an urgent review of anti-terror law.
"While congratulating the police in bringing this case to a successful conclusion we now need to look again at the law to ensure that it allows no gaps that permit preachers of hate to undertake their activities under the cloak of freedom of speech exercised in a democracy," he said.
"In future we need to show zero tolerance to those who act and behave in this way."
Police argued that many people tried for terror offences had been influenced by Choudary's sermons where he called for Islam to "dominate the whole world".
In one speech in March 2013 he said: "Next time when your child is at school and the teacher says 'What do you want when you grow up? What is your ambition?', they should say 'To dominate the whole world by Islam, including Britain - that is my ambition'."
Home Secretary Amber Rudd said: "These dangerous individuals were recruiting sergeants for Daesh.
"They poisoned the minds of vulnerable people and their warped and twisted propaganda offered support and succour to a murderous and barbaric terrorist organisation."
She added: "The Government is clear. We will continue to confront those who promote hate and threaten our way of life.
"Together we will protect communities from extremism and defeat this toxic ideology."
