Hamza, 47, was convicted on Tuesday on 11 counts including soliciting murder, stirring up racial hatred and possessing a training manual "of use to terrorists" and given a seven-year prison sentence.
Police said north London's Finsbury Park Mosque, which Hamza ran from 1997 until 2003, had links to some of the most important terrorism cases of the last decade.
Hamza was arrested in 1999 over his suspected involvement in a kidnapping of Western tourists in Yemen but no action was taken against him until May 2004 when he was arrested on a US extradition warrant over alleged terrorism offences.
Media and politicians queried why it had taken so long for the radical cleric to be prosecuted.
"Why on earth did police leave Hamza untouched for so long?" the
Daily Mail asked in an editorial.
Both Conservative and Labour politicians said the police's tolerant attitude to Islamic militants before the September 11, 2001, terrorist attacks on the United States had allowed extremism to grow.
"The remarkable thing is why it took so long to bring this prosecution, especially when much of the evidence was known about years ago," said Conservative home affairs spokesman David Davis.
Hamza investigated
Although police never linked Egyptian-born Hamza directly to any specific plot, they had long said his mosque acted as a base for militants.
Worshippers at Finsbury Park included "shoebomber" Richard Reid and September 11 plotter Zacarias Moussaoui.
Scotland Yard said they had "thoroughly investigated" complaints against Hamza between 1999 and 2004.
"The police, following detailed and thorough investigations, made three formal submissions of evidence to the CPS (Crown
Prosecution Service)," said a joint statement from Sue Hemming, the head of the CPS's counter terrorism division, and the head of the police's anti-terrorist branch Peter Clarke.
The police and the CPS issued the joint statement in response to criticism that action had not been taken sooner, and said the conviction of Hamza was the outcome of a “close and painstaking” joint effort, the BBC reported.
"Two of these (submissions) were in relation to potential offences committed in the Yemen, the second also included evidence relating to a website.
"The third submission was in relation to this trial."
They said the submissions relating to the Yemeni probe and the website had been "carefully reviewed by experienced, senior prosecutors" and there had been insufficient evidence.
"On the third occasion, there was sufficient evidence and the case has been prosecuted successfully," the statement said.
Newspaper reports said three of the suicide bombers who attacked London's transport system on July 7 last year, killing 52 people, had also spent time at the mosque.
"We have no evidence at this stage those involved had any connection with Abu Hamza," a police spokesman said.
Tighter laws
Prime Minister Tony Blair told parliament that planned laws would help police deal with those who spoke in support of terrorism.
"Indirect encouragement to acts of terrorism will be made unlawful and glorification will be mentioned specifically as an example of indirect incitement to terrorism," he said.
He called for the Conservatives to drop their opposition on freedom of speech grounds, to plans to proscribe groups that glorified terrorism.
"I think it is very important we send a very strong signal out that any group or people who glorify terrorism in any way at all will be committing a criminal offence," he said.