While schools have put in place measures to counter radicalisation from Islamic extremists, “the real gap” is with in parents’ knowledge of the internet, the London Assembly was warned on Tuesday.

Many isolated communities may not understand the reach of modern social media with parents believing their children are safe simply because they are home.

Initiatives such as the Prevent strategy, drawn up after the 7/7 attacks, allows teachers to “push back” against propaganda from Islamic terror groups such as Isis.

But, the police and crime committee was told, measures aimed at improving community cohesion were undermined by the internet which turned every bedroom into a potential recruitment office.

The families of three Bethnal Green schoolgirls who made their way to Syria all expressed surprise they had been radicalised without their knowledge.

Shiraz Maher, from the International Centre For The Study Of Radicalisation And Political Violence said: “It’s all well and good to have the schools being up on [the dangers] but it’s clear that individuals are at home communicating with fighters in Syria. They’re doing that from iPads, from mobile phones, from laptops.

“To their parents’ minds they’re at home, they’re under watch, so they feel like there’s not a problem.

“There are parents who are not particularly savvy about the way technology can be used and the next thing they know their children are turning up having crossed the Syrian border.

“That is hugely distressing – but all the tell-tale signs were there.”

Sahima Begum, right, sister of Shamima Begum leaves Parliament with Abase Hussein, left, father Amira Abase after discussing their relative's radicalisation

He said that giving parents confidence in the system was key. Parents who have engaged with the police have seen their children given lengthy jail sentences “which is hugely counter-productive”.

“There needs to be a system that allows parents to come forward to work with the police or with other agencies to achieve the best outcome for the children without criminalising them.”

Diane Egan, Havering community safety team leader, said: “[We need to] equip parents to deal with online safeguarding. If you can get that right it covers a whole remit of issues not just radicalisation but sexual exploitation too.”

She said she ran parents’ evenings within schools to teach parents what they children can access. “We’ve had a real appetite from parents who know nothing about the internet but want to protect their teenagers.”

Martin Esom, chief executive of Waltham Forest said counter-terrorism initiatives used to be focussed on influential ringleaders in the community.

“The big change is that you don’t need those individuals any more because there’s a whole broadcast medium that’s reaching out into children’s computers.

“When the Government talks about banning venues – that’s important – but what you’ve got, in effect, is a venue in every house.”