Anjem Choudary has been released from prison after serving half of the five-and-a-half-year sentence he received in 2016 for urging support for Isis and pledging allegiance to the terrorist group.

Choudary, 51, who was a key figure for a succession of extremist Islamist groups, emerged early on Friday morning from Belmarsh prison in south-east London.

Authorities have been making preparations to stop him from inciting support for terrorism and he will in effect be banned from making any public statements or speaking with the media.

Before the release, the prisons minister, Rory Stewart, said Choudary, from Ilford in east London, remained a “genuinely dangerous” figure and that the “completely pernicious” cleric would be watched “very, very carefully” by police and security services.

However, the Metropolitan police’s former assistant commissioner and former national lead for the UK’s counter-terrorism policing said on Friday morning it was important not to overstate Choudary’s significance.

Mark Rowley, who was serving in the role when Choudary was prosecuted, said: “At the end of the day he is a pathetic groomer of others. That is what he has done in the past. He is not some sort of evil genius we all need to be afraid of,” he told BBC Radio 4’s Today programme.

“I think we have to recognise that radicalisers look to generate a profile, look to prey on the vulnerable and we need to be thoughtful about how we report their activity.”

Rowley criticised the way he said social media companies appeared to elevate the significance of figures such as Choudray, adding: “It’s pretty depressing if you Google ‘UK Muslim spokesman’ and he comes up as the first hit.

“For goodness sake, we have a very impressive Muslim mayor of London, a Muslim home secretary and he comes up as the first hit. On YouTube he is four of the first 10 videos.

“That is giving him a profile because these companies chase your attention through the salacious and contentious rather than through anything accurate or responsible. That is the disgrace in this and it gives people like him, who is a sad individual, more credibility and more attention than they deserve.”

Rowley said “work was being done” to get the US to tweak legislation so that silicon valley tech companies altered their treatment of radical hate speech in line with what home secretaries had been pushing for. He predicted the next decade would see a mix of “persuasion, balanced with regulation” because it would take a lot to change the way firms such as YouTube operated.

UK officials believe they have drafted conditions that will stop Choudary from repeating his method of encouraging support for extremism, which enabled him to escape prosecution for years even as his propaganda motivated at least 100 people to pursue terrorism.

In prison, he was offered counselling to try to change the views that led to his conviction. It is not known if those efforts were successful, but his release halfway through his sentence shows that, despite his past pronouncements denouncing western authorities, he observed prison rules.

