Notorious hate preacher Anjem Choudary could be released by the end of next year, having served less than half of his sentence, it has emerged.
Choudary was jailed last September for five-and-a-half years after he was convicted of inviting support for a proscribed organisation while he lived on taxpayer handouts.
Due to the time he spent on remand awaiting sentence – almost five months – Choudary could be back spreading hate as soon as December 2018 and no later than the end of January 2019.
Notorious hate preacher Anjem Choudary could be released by the end of next year, having served less than half of his sentence, it has emerged
The revelation could be problematic for the security services, who have disclosed they are currently handling 500 active investigations.
The extremist, who founded the group al-Muhajiroun, is believed to have inspired the 7/7 bombers and has been linked to the Westminster attacker Khalid Masood.
It is also thought that Choudary aided 110 British jihadists to travel to Syria in order to fight for Islamic State.
Despite being known to spread hate, Choudary was given a platform to speak by the BBC and controversially appeared on Newsnight in 2013.
Choudary was jailed last September for five-and-a-half years after he was convicted of inviting support for a proscribed organisation while he lived on taxpayer handouts
Then, he refused to condemn Michael Adebolajo after he killed fusilier Lee Rigby.
Hannah Stuart, author of Islamist Terrorism, a definitive analysis of UK attacks and offences, said his release would be a 'massive headache'.
She told The Telegraph: 'When Theresa May talks about longer sentences for terrorists, she will have had in mind extremists like Choudary who are accused of such offences as disseminating terrorist material and glorifying terrorism.'
Despite his ideas spawning a generation of home-grown terrorists and enraging the British public, Choudary had previously thwarted authorities by managing to stay on the right side of the law.
But a pledge of allegiance posted online provided a turning point for police who swooped to arrest British-born Choudary and his deputy Mohammed Mizanur Rahman.
Rahman, who was described as a 'hothead' by the judge, was also given a sentence of five years and six months.
The judge said both men were 'dangerous' and had shown no remorse for what they had done.
The judge described Choudary (left) as 'calculating' and Rahman (right) as a 'hothead'
Their trial heard Choudary swore an oath of allegiance to ISIS leader Abu Bakr al-Baghdadi in an East London pub after the so-called 'caliphate' was declared in the Middle East.
He and his deputy then pressed upon Muslims their supposed obligation to 'make hijrah', meaning to travel to ISIS-occupied lands, the court heard.
Choudary rose to notoriety as the mouthpiece of Omar Bakri Mohammed - a Syrian extremist who founded the banned extremist group al-Muhajiroun (ALM).
Choudary 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, from Ilford, north-east London, set out his ambitions for the Muslim faith to 'dominate the whole world'.
Choudary pictured with an image of Buckingham Palace imagined as a mosque
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".'
His supporters included Michael Adebolajo and Michael Adebowale, the murderers of Fusilier Lee Rigby, and suspected ISIS executioner Siddhartha Dhar.
Shortly after the announcement of the caliphate, Choudary held a meeting with his closest aides at a curry house in Mile End Road in east London to discuss it.
Before accepting it was legitimate, he also consulted his 'spiritual guide', 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 posted on the internet, which stated the Muhajiroun had 'affirmed' the legitimacy of the 'proclaimed Islamic Caliphate State'.
Choudary, pictured in a file photo, smiled as his sentence was announced today
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 married 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, 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.'
Following the convictions, Commander Dean Haydon, head of Scotland Yard's counter-terrorism command, said: 'These men have stayed just within the law for many years.
Choudary's conviction was welcomed by leading British Muslims, who condemned his 'evil' and 'hateful' views. He is pictured at the Holiday Inn in Chingford
'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.'
Commander Haydon added: '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.'
Choudary's conviction was also welcomed by leading British Muslims, who condemned his 'evil' and 'hateful' views.
After his conviction, Choudary's Twitter account was removed by the social media giant.