Hate preacher Anjem Choudary, who helped radicalise a string of terrorists including soldier Lee Rigby's killers, is facing years in jail for drumming up support for Islamic State.
The British-born 49-year-old encouraged backing for the terrorist group in a series of talks posted on YouTube, and recognised a caliphate - a symbolic Islamic state - had been created under an IS leader after it was announced on June 29 2014, the Old Bailey heard.
Despite being a leading figure in the banned group al-Muhajiroun (ALM), and a series of former supporters going on to be convicted of terrorism, Choudary stayed on the right side of the law for two decades before investigators were able to pin him down.
Choudary and co-defendant Mohammed Mizanur Rahman, 33, were found guilty of inviting support for IS between June 29 2014 and March 6 2015. The verdicts were delivered on July 28, but for legal reasons can only be reported for the first time today.
As the pair were convicted, Mr Justice Holroyde said they had only shown "a grudging compliance" to the court, adding: "You have made your disregard for the court abundantly plain."
Choudary faces a maximum possible sentence of 10 years in prison, although the judge admitted: "There is very little in the way of precedent in the way of sentencing. Although this has been an offence under an Act of Parliament for some time, it's very far from being one of the most common."
Police pounced after Choudary, along with three other influential radicals, lent their names to an oath of allegiance to IS which was posted on the internet.
The trial heard that the preacher, viewed by officers as a key force in radicalising young Muslims, had been the "mouthpiece" of Omar Bakri Mohammed - the founder of the banned extremist group ALM.
He courted publicity by voicing controversial views on Sharia law, while building up a following of thousands through social media, demonstrations and lectures around the world.
In one speech in March 2013, Choudary set out his ambitions for the Muslim faith to "dominate the whole world".
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'."
Supporters included Michael Adebolajo and Michael Adebowale, the murderers of Lee Rigby, and suspected IS executioner Siddhartha Dhar.
Shortly after the announcement of the caliphate, Choudary held a meeting with his closest aides at a curry house on the Mile End Road in east London to discuss it.
Before accepting it was legitimate, he also consulted his "spiritual guide" Omar Bakri Mohammed, currently in jail in Lebanon, and Mohammed Fachry, the head of ALM in Indonesia.
On July 7 2014, the trio's names appeared alongside Rahman's on the oath, which stated the Muhajiroun had "affirmed" the legitimacy of the "proclaimed Islamic Caliphate State".
The defendants followed up by posting on YouTube a series of lectures on the caliphate, which Choudary promoted to more than 32,000 Twitter followers.
The father-of-five denied encouraging his followers to back the terror group and insisted the oath had been made without his knowledge. He said of the pledge: "It is completely unnecessary. For the rest of the Muslims it is obedience from the heart."
Despite protesting his innocence, he continued to express extreme views during his Old Bailey trial, refusing to denounce the execution of journalist James Foley by so-called Jihadi John, aka Mohammed Emwazi, in Syria in 2014.
He told the jury: "If you took an objective view there are circumstances where someone could be punished."
Choudary, of Hampton Road, Ilford, and Rahman, of Sidney Street in Whitechapel, east London, will be sentenced on September 6.
Commander Dean Haydon, head of Scotland Yard's counter terrorism command, 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.
"This has been a significant prosecution in our fight against terrorism and we will now be working with communities to ensure that they are not replaced by others spreading hate.
Sue Hemming, of the Crown Prosecution Service, said: "These two 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.
"Both men were fully aware that Daesh is a proscribed terrorist group, the brutal activities they are carrying out and that what they were doing was illegal. Terrorism can have no place in our society and those that encourage others to join such organisations will be prosecuted."
Choudary's conviction was welcomed by leading British Muslims who condemned his "evil" and "hateful" views.
Imam Qari Asim, senior imam of Leeds Makkah Mosque, said: "We have to be very careful of those who look to spread a hateful ideology by preying on vulnerable individuals to lead them down a violent path."
Kashan Amar, network co-ordinator of Birmingham based group Upstanding Neighbourhoods, said the organisation was formed to counter Choudary's "evil messages".
He said: "His distorted world view and hateful vision have led to him facing time in prison.
"There is no place for individuals like him in our community and I am glad to see his pariah status confirmed. It is an important moment in our Say No To Anjem Choudary campaign which has always been clear that his rhetoric encouraged the support of terrorists."
Imam Irfan Chishti, imam of Manchester Central Mosque, said: "British Muslims across the UK welcome this verdict. The community has been unanimous in its rejection of these individuals and everything they stand for.
"This conviction demonstrates the influence of these hateful views together with the power they had over people by encouraging them not to think for themselves. We shouldn't be complacent that these convictions will be the end of young people being targeted."