GETTY Scotland Yard were prevented from arresting Choudary because MI5 used him for intelligence

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Counter terror officers believed they had enough evidence to build a case against the radical Islamic State sympathiser but were reportedly blocked from doing so because he was a vital part of MI5’s ongoing investigation. The controversial situation led to a build-up of tension between the two sides with police feeling “frustrated” that Choudary was not being brought to justice, according to a source.

Serious questions were raised as to why Choudary was allowed to continue spreading his Islamist poison across Britain for more than 20 years, but now a counter terror source has said MI5 were responsible. Following his conviction of inviting support for ISIS it emerged Choudary was involved in at least 15 terror plots dating back as far as 2001.

Police also believe he has connections to around 500 of the 850 young British Muslims who have left the country to join-up with ISIS jihadis. The source said: “I am gobsmacked that we allowed him to carry on as long as long as he did. "He was up to his neck in it but the police can't do full investigations on people if the security service say they are working on a really big job, because they have the priority. “That is what they did constantly. While the police might have had lots of evidence they were pulled back by the security service because he [Choudary]was one of the people they were monitoring. “It was very frustrating and did cause some tension but we were told we had to consider the bigger picture.”

GETTY Anjem Choudary pledged allegiance to ISIS before his arrest

Security expert Will Geddes claims MI5 and Scotland Yard have a solid track record of working together, but tensions can sometimes arise when it comes to prosecuting and obtaining intelligence. He said: “Whilst the cops always want the collars the spooks want the information and it is a challenge getting the right balance. “Choudary was certainly clever and knew where the line was and that was part of the reason it took so long to get him, but it was certainly possible that MI5 wanted to continue to monitor him because he was the focal point of so much. “Given how influential he was in terms of setting up the forums for those guys to get inspired, it made perfect sense for the intelligence agencies to say ‘we haven’t exhausted this yet’. “In the end though he got caught because he believed his press too much and he got carried away with his own media profile.”

GETTY MI5 blocked Scotland Yard from arresting Choudary, a source said

Raffaello Pantucci, a terrorism expert at the Royal United Services Institute, said: “Intelligence officers have to generate leads somewhere, so if you have got a kind of honeypot that is Anjem Choudary and every nutter in the UK is gravitating towards him and from there you just trail them and follow them, you can see how it’s doing your job for you in some ways. “There is undoubtedly an element of security folk who work in the intelligence side who would probably see this as something that is potentially quite useful.” But he said he believed the authorities had always intended to convict Choudary as soon as they had a strong enough case to take him out.

Anjem Choudary: Sentenced to 5 years and 6 months for encouraging support for ISIS Tue, September 6, 2016 Anjem Choudary is a British Muslim social and political activist, as well as the spokesman for Islam4UK. We take a look at his protests in pictures that have been at the centre of controversy and global debate Play slideshow Getty Images 1 of 15 Islam4UK Spokesman Anjem Choudary leaves a press conference in Millbank Studios on January 12, 2010. The radical Islamic group had planned to stage a march through Wootton Bassett to honour Muslims who have been killed in the conflict in Afghanistan