Amid growing incidents of British children travelling overseas to join the Islamic State, Prime Minister David Cameron on Monday unveiled tough new measures, allowing parents of teens at risk of "poisonous" radicalisation to have their passports blocked.
The new rules announced in London also include a full review of all public institutions in the country to safeguard them against infiltration by extremists, including schools, colleges, the civil service and local authorities.
More parents will be able to ask for their children's passports to be cancelled if they fear they could go overseas to join terror groups.
The power already covers under-16s, but will be widened to 16 and 17-year-olds.
"The government's new counter-extremism strategy is a clear signal of the choice we have made to take on this poisonous ideology with resolve, determination and the goal of a building a greater Britain. And a key part of this new approach is going further to protect children and vulnerable people from the risk of radicalisation by empowering parents and public institutions with all the advice, tools and practical support they need," Cameron said.
Families can contact a passport office where officials will investigate their concerns before a final decision is taken by UK home secretary Theresa May.
As part of the new measures, anyone with a conviction for extremist activity will also be automatically barred from working with children and vulnerable people under the plans.
"We know that extremism is really a symptom; ideology is the root cause -- but the stakes are rising and that demands a new approach. So we have a choice -- do we choose to turn a blind eye or do we choose to get out there and make the case for our British values,” Cameron added.
"If you talk to, as I have, parents of young people who have been on the path to radicalisation, or perhaps parents, as I have heard from, who have children who have gone out to Syria, some of whom have died out there fighting, then they are saying that they want to see more action taken," May told BBC.
"I'm not pretending that any of this is easy. Of course this is difficult, but government has a choice here. We can either say 'well, this is difficult so let's not do anything' or we can say 'well, actually it is difficult, but this is so important that we need to take action'," she said.
The new powers, revealed in Cameron's counter-extremism strategy, build on those he set out in July to force public sector organisations to boycott groups or individuals listed as extremist, introduce "extremism disruption orders" on those seeking to radicalise young people online, close mosques where extremist meetings have taken place and strengthen the powers available to the media regulator, Ofcom, to sanction channels that broadcast extremist content.
The prime minister also announced in his Conservative party conference speech earlier this month that madrasas and other religious bodies that teach children intensively would face inspection.
Writing on Facebook, Cameron said the government "needs to support Muslims who are confronting the extremist narrative and providing a positive alternative".
"They can show the boy in East London or the girl in Birmingham how proud you can feel to be both British and Muslim, without conflict or contradiction. And in standing up, by speaking out, I am confident that we will defeat the extremists, and together build the greater Britain that is within our grasp," his post read.
The counter-terror strategy includes measures such as bans on radical preachers posting material online, closure orders for law enforcement and local authorities to close down premises used to support extremism, and demands that internet service providers do more to remove extremist material and identify those responsible for it.
Secretary-general of the Muslim Council of Britain Dr Shuja Shafi accused Cameron of a "misguided" approach.
Dr Shafi said in a statement: "Whether it is in mosques, education or charities, the strategy will reinforce perceptions that all aspects of Muslim life must undergo a 'compliance' test to prove our loyalty to this country. These measures could be seen more as a means to address the anxieties a minority of people may have against Muslims and their religious life, rather than the scourge of terrorism itself."
British police estimate at least 700 people, including many children, from the UK have travelled to support terror linked organisations in Syria and Iraq, such as the Islamic State.