Anjem Choudary has been convicted of inviting others to support ISIS after a secret trial in July.
The 49 year old radical preacher – who enjoyed little support within the Muslim community but whose voice was amplified by the mainstream media – had stayed “just within the law” for years, but was arrested in 2014 after pledging allegiance to the terrorist group.
Many people tried for serious terror offences were influenced by his lectures and speeches, police said.
Choudary was convicted alongside confidant Mohammed Mizanur Rahman.
Counter-terrorism chiefs blame the father-of-five, and the proscribed organisations which he helped to run, for radicalising young men and women.
Both men were charged with one offence of inviting support for ISIS – which is contrary to section 12 of the Terrorism Act 2000 – between 29 June 2014 and 6 March 2015.
The verdict on the two defendants was delivered on 28 July, but can only be reported now following the conclusion of a separate trial at the Old Bailey of another group of men for a similar offence.
The trial heard how the men decided in the summer of 2014 that ISIS had formed a “Khilafah”, or Islamic state, that demanded the obedience and support of Muslims.
They then invited others to support ISIS through speeches and announced their own oath of allegiance to its leader. The oath of allegiance was a “turning point” which meant they could be put on trial, the Met Police said.
Choudary was once the spokesman for al-Muhajiroun and has become one of the most influential “radical preachers” in Europe. A string of his followers have either left the UK to fight in Syria or tried to do so.
When ISIS announced a “Khilafah” – an Islamic state – in June 2014, the court heard that Choudary held a meeting with his closest aides at a curry house in east London.
Before accepting the “Khilafah” was legitimate, the jury heard he consulted his “spiritual guide” Omar Bakri Mohammed, who is currently in jail in Lebanon.
On 7 July 2014, the men’s names appeared alongside Rahman’s on the oath, which stated al-Muhajiroun had “affirmed” the legitimacy of the “proclaimed Islamic Caliphate State”.
During his trial Choudary also refused to denounce the execution of journalist James Foley by Mohammed Emwazi, nicknamed Jihadi John, in Syria in 2014.
“If you took an objective view there are circumstances where someone could be punished,” he told the jury.
Supporters of Choudary included:
■ Michael Adebolajo and Michael Adebowale, the murderers of soldier Lee Rigby
■ Suspected IS executioner Siddhartha Dhar
■ Omar Sharif, a British man who attacked Tel Aviv in 2003
■ Brusthom Ziamani, jailed 12 years later for planning to kill in the streets of London
The trial also heard that Rahman – previously convicted of soliciting to murder – went on Facebook to tell his followers that migration to ISIS territory was a “duty”.
“Let’s be clear, the Muslims in the Khilafah need help,” he wrote, after communicating with a British fighter who urged him to find recruits.
“The one who is capable to go over and help the Muslims, must go and help.”
Fight against terrorism
Commander Dean Haydon, head of the Met Police’s counter-terrorism unit, said the case which led to the conviction of Choudary and Rahman was a “significant prosecution in our fight against terrorism”.
He said: “These men have stayed just within the law for many years, but there is no-one within the counter-terrorism world that has any doubts of the influence that they have had, the hate they have spread and the people that they have encouraged to join terrorist organisations.
“Over and over again we have seen people on trial for the most serious offences who have attended lectures or speeches given by these men.
“The oath of allegiance was a turning point for the police – at last we had the evidence that they had stepped over the line and we could prove they supported ISIS.”
He said the trial had considered over 20 years’ worth of material over more than 333 electronic devices containing 12.1 terabytes of storage data.
Sue Hemming, head of counter-terrorism at the Crown Prosecution Service, said the men “knowingly sought to legitimise a terrorist organisation and encouraged others to support it”.
“They used the power of social media to attempt to influence those who are susceptible to these types of messages, which might include the young or vulnerable,” she added.