Parents concerned that their 16 and 17 year old children are at risk of travelling abroad to join Islamic State (Isis) will soon be able to apply to have their passports removed.

David Cameron will today warn that the "stakes are rising" in the battle against extremism as he unveils measures to prevent young people being radicalised.

It is thought at least 700 young people have travelled from Britain to become involved in fighting in Syria.

They include Aqsa Mahmood, from Glasgow, who is thought to have married an Isis fighter.

Her decision left her family feeling 'betrayed' after their daughter had been radicalised by extremist ideology online.

Ruhul Amin, an Islamist militant from Aberdeenshire, who was killed in an RAF drone strike in August is also among those who have travelled to the war-torn country.

The plan will see an extension of powers for passports to be withdrawn from young people at risk of travelling abroad to join groups such as Isis.

The mechanism has already been used on several under-16s since it was introduced in July, according to Downing Street, and will now be available for 16- and 17-year-olds.

There will be bans on radical preachers posting material online. Internet firms are to work more closely with police to stop extremist material being disseminated.

Anyone with a conviction or civil order for terrorist or extremist activity will also be automatically barred from working with children and vulnerable people.

The Prime Minister, who over the weekend announced an extra £5 million would be ploughed into moderate Muslim groups and charities this year, is to reiterate his view that defeating Islamist extremism is the "struggle of our generation".

"It is one of the biggest social problems we need to overcome," he will declare. “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?

"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 building a greater Britain.”

He will add: "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."

It is thought Mr Cameron will pledge to act on a review of sharia courts and declare that all new arrivals to the country should respect "British values".

In a foreword to the strategy, Home Secretary Theresa May defines these as "democracy, free speech, mutual respect and opportunity for all".

Andy Burnham, her Labour Shadow, described extremism as the “greatest challenge of our age” and said it was right for the Prime Minister to focus on it.

"For our part, we will always support measures that are reasonable, proportionate and evidence-based. But we have a job to ensure that, in this difficult area, the Government gets the balance right and doesn't go beyond that,” he said.