LONDON — At London’s Ladbroke Grove Tube station, a very steep set of stairs leads down to street level. If you turn right at the foot of the stairs it is only a short stroll to the famous Portobello Market and the even more famous Nottinghill, with its pubs and clubs, designer shops and cream and pink candy-colored house frontages. No other part of London is as cool and effortlessly chic.

If you were to turn left at the foot of the stairs, you would find a world that is a few shades darker. A few kilometers down that road is the Quintin Kynaston Academy, where Mohammed Emwazi went to school. Emwazi is better known as "Jihadi John," famous for cutting off people’s heads on live TV in the middle of the Syrian desert. He swears that "with Allah’s help, ISIS will be slaughtering your people in your streets soon."

"When there is no enemy within, the enemies outside cannot hurt you," Winston Churchill once said. But this does not hold true on London’s streets and has not done so for a while. More than 600 young Britons have joined the ISIS terrorist network. The group's tentacles can reach anywhere, into every corner — into Islamic cultural institutions, into mosques, even into children’s bedrooms.

ISIS recruiters stalk young boys and girls by spying on their online entries. They take advantage of their young victims' naïveté and lack of self confidence. In the last year alone, at least 22 young girls gave up their lives in the United Kingdom to become "jihadi brides."

"Dad, I am a member of ISIS and I will never return home." That is how the last phone call of one of those girls made to her father ended.

"I don't preach"

At the all-girls Sion-Manning School, a group of 150 students are howling with laughter, screaming in a way that only teenagers can scream. Humza Arshad has just told his first joke — "But you always get such dry ankles in the desert! Honestly, have you ever looked at the ankles of those jihadists? Don’t they have E45 cream down there?" — and it went down well.

"Hey girls, how many of you are Muslim?" More than a third lift their hands. "Cool, we're this place over!" More shrieks of laughter. The girls know Humza. He is a YouTube star, with nearly 250,000 followers. And more than 60 million people have watched his clips online.

The son of Pakistani immigrants, he has become London’s newest and most modern weapon in the fight against Islamic extremists. The 29-year-old comedian is touring more than 50 schools, by order of the Metropolitan Police. More than 20,000 kids have seen "badman," aka Humza, have cheered him in their assembly halls, have cheered the man dressed in a beanie hat and hoodie who slags off ultra-conservative Pakistani parents and "remote-controlled" ISIS followers.

But the message he wants to deliver at the end of his gigs is a simple one: Islam is a peaceful religion. He says that people who view violence as a means to an end have misunderstood Islam's message. "I don’t preach," the comedian insists. "But I can reach the children much better than a civil servant in a checked shirt can."

Star power

Riz Chothia is a civil servant who was inspired to hire Humza when he saw his 11-year-old son watching "badman" online. "This was a young Muslim, who is incredibly popular, and whose sketches you wouldn’t have to fear as a parent," he explains. "That was it!"

Chothia is a police officer and part of a special anti-terrorism task force in Lincolnshire, in England's midlands. After he hired Humza, the policeman's colleagues in London followed suit. "With Humza we had somebody who speaks the language of the youth of today, someone who can reach them far better than we can," says Chothia.

At Humza’s gigs there are no police officers in uniform, not even the logo of the Met is anywhere in sight. No enforcement gigs, no monologues. Instead, Humza’s gigs resemble "Q&A game sessions." What can young people do when a friend or relative is acting strangely all of a sudden? Humza tries to get the message across that it's okay to contact the police in these situations.

With every passing minute the girls become more and more restless. Humza has promised them the opportunity to take pictures with him at the end of the gig. A little while later, a wave of girls accosts him and, cell phone camera's popping, a huge selfie session begins.

Afterwards – Humza has been gone for quite a while ago at this stage – the girls are still standing together in groups, chatting and giggling with flushed faces. The photos featuring them together with Humza have long since disappeared into the online ether that is Instagram. But the message has taken hold in the girl’s heads and they are still thinking about it.

"This was the first time someone ever explained to me what extremism actually is," says Shania, 15. "And he also explained what I can do if I witness it."