More than 3,500 miles away, in the British seaside town of Lowestoft, single father Ivan Humble was helping form the English Defence League (EDL).
For years, the two men fought ideological battles on opposing sides, using each other’s groups to accelerate a cycle of radicalisation spreading across the English-speaking world.
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Mr Humble’s campaign against Choudary’s extremism morphed into broad anti-Muslim hatred, while Mr Morton’s writings inspired terrorists including the London Stock Exchange bomb plotters and the man who planned to blow up the Pentagon.
In 2011, both their journeys were brought to an end. Mr Morton was arrested and jailed for threatening the creators of animated TV sitcom South Park for mocking the prophet Muhammad.
In the UK, a chance meeting with a Muslim started a process of dialogue that led Mr Humble to quit the EDL.
Now, both men have joined forces to fight both Islamist and far-right extremism by using their experience to prevent others from following the same path.
Speaking to The Independent, they warned that authorities “haven’t learned the lessons” of the chain reaction sparked by Choudary and his followers in the Noughties, and were letting extremism rise once more.
Mr Humble compared Choudary’s tactics, which let him avoid prosecution for years by dodging terror and hate speech laws, to that of growing white nationalist groups.
“We haven’t learnt the lessons from Choudary,” he said. “We let him carry on giving those messages for years.”
A neo-Nazi terror attack that left two people dead in the German city of Halle last week sparked fresh warnings over the “great replacement” conspiracy spread by groups like Generation Identity.
The suspect named “declining birth rates” among whites among his key motivations, and the same theory drove the attacks in Christchurch, Poway, El Paso and Norway.
But counterterror police have admitted they have “no plan” to respond to the ideology as long as its proponents stop short of openly calling for violence.
Mr Morton said the far right was now “going transnational” in a manner mirroring Islamist ideologues in the Noughties.
“The narrative uniting everyone is the great replacement theory,” he said. “That is the glue starting to allow people who are predominantly white to get a foot on a transnational network.”
Mr Morton said he had observed both far-right extremists and Islamists trying to use the Christchurch attack to incite more atrocities in online forums.
“Islamists share the video as a message [showing Muslim victims being shot inside mosques] calling for revenge,” he added.
“There was a chat the other day like, ‘when are we going to take revenge for Christchurch, when are we going to respond?’”
The Halle attacker is one of several gunmen believed to have been inspired in part by Brenton Tarrant, whose manifesto and livestream is still being widely shared online alongside those posted by other white supremacist terrorists.
Mr Humble believes the great replacement narrative, which states that white people are being “replaced” by non-whites in western nations, is making the current British far right increasingly extreme.
“Everybody at the moment seems to be looking at Tarrant as their inspiration to a point,” he said. “It’s more acceptable to become a terrorist.”
He said extreme right-wing groups in the UK have been looking for something to “fuel their fire” in the wake of the 2017 Isis-inspired terror attacks and were currently latching onto Brexit to drive protests.
Mr Humble was radicalised after becoming angry over provocative stunts by Choudary’s al-Muhajiroun* (ALM) Islamist network, which sparked the formation of the EDL.
The 48-year-old got involved in the group two weeks before it was formed in 2009, after becoming enraged by news coverage of an ALM protest at a homecoming parade for British soldiers in Luton.
Wearing traditional Islamic dress, the demonstrators hurled abuse at the troops, calling them terrorists and holding signs denouncing the soldiers as “butchers of Basra” and “baby killers”.
Mr Humble, who was supporting a charity helping injured soldiers and amputees, posted an angry Facebook status that saw him approached online by EDL organisers.
“We felt we were standing up to Choudary and the radicals,” he said. “Being trapped in the echo chamber I went from hating radicals to all Muslims. The media was holding Choudary up as the voice of the Muslim community, even after the death of Lee Rigby he was on the TV.”
Mr Humble said ALM’s high-profile provocations and protests “reinforced everything” he thought about Muslims, as he rose up the EDL’s ranks to become the regional organiser for East Anglia.
He fears they drove a permanent change in the British public’s perception of Islam, as years-old ALM stunts and campaigns are recycled on the internet as supposed proof of the “Islamisation” of Britain.
“They overlooked Choudary for too long and it will do damage for years to come,” he added.
Mr Morton said the link between ALM and the EDL was evidence of the “symbiotic relationship between jihadism and right-wing extremism”, adding: “ALM’s impact went far beyond the terrorist threat it posed.”
He was in contact with Choudary and other ALM leaders when they were planning protests including the infamous 2010 Armistice Day poppy burning, and recalls discussions of how media coverage could be used to “fragment society” on both sides of the Atlantic.
He said Islamist groups linked to Choudary were “well aware” that their activities were driving support to the far right, and actively used the EDL and other groups in their own propaganda.
“One of the primary strategies was to get on TV, which was very easy – particularly if you were able to do provocative things to reap the ire of the far right,” Mr Morton said.
“It became increasingly easy to antagonise them and anti-Muslim sentiment started to grow over here [in the US] as well.”
Mr Morton said Choudary was a “master at creating widespread polarisation” and deliberately let his own extreme views be presented as that of all Muslims in the UK.
He said Islamists and the far right “still play off against each other”, and that a “civil war-like atmosphere” in politics on both sides of the Atlantic was fuelling both sides.
The Columbia University graduate converted to Islam in 2000 and came into contact with ALM’s American offshoot in 2004.
The Islamic Thinkers Society, which was calling for a global Islamic state, put Mr Morton in touch with high-profile Islamists including Choudary, Jamaican preacher Abdullah el-Faisal and al-Qaeda propagandist Anwar al-Awlaki, who was killed in a 2011 drone strike.
In 2007, he and fellow extremists started their own group – Revolution Muslim – and continued street preaching while running a website featuring al-Qaeda propaganda.
Two years later, Mr Morton launched the Jihad Recollections magazine, which is seen as a precursor to al-Qaeda’s Inspire and Isis’s glossy Dabiq and Rumiyah publications.
But in 2011, he was arrested and jailed after a follower made threats against the creators of South Park for mocking the prophet Mohammad.
Mr Morton, who then went by the name Younes Abdullah Mohammed, became an FBI informant in prison and was freed early in 2015.
Now, working with Mr Humble and other former radicals, he is using the propaganda format he pioneered to challenge jihadis and the far right by releasing counterextremist magazines through his Parallel Networks organisation.
Mr Morton plans to spread the publications, which are formatted to appear identical to radical literature, in online chat groups used by extremists.
They hope to penetrate online echo-chambers of the kind where Mr Humble said he was “brainwashed” by challenging dominant narratives.
The pair said the dialogue and friendship they have forged gives them hope for current extremists.
Mr Humble said he never could have imagined working with a former jihadi while in the EDL, but that they had “clicked” over their shared radicalisation by Choudary.
Mr Morton hopes their personal dialogue could be scaled up into a wider discourse between Islamist and the far right, adding: “They’re much more similar than they are different.”
*Al-Muhajiroun (ALM) has been used in this article to describe all incarnations of Choudary’s Islamist network, which operated under names including al-Ghurabaa, Islam4UK, Islamic Path and Muslims Against Crusades