David Cameron has said the UK should “step up and do more” in the fight against Isis in Iraq and Syria, in the clearest sign yet that he is committed to sending UK forces to join US-led air strikes in Syria.

Speaking to the US television network NBC on Sunday, the prime minister said he would “have to take my parliament with me” but that he wanted to “destroy this caliphate, whether it is in Iraq or in Syria”.

“I want Britain to do more,” he said. “Be in no doubt, we’re committed to working with you to destroy the caliphate in both countries.”

The House of Commons voted against military action in Syria in 2013 and parliamentary authorisation has so far only been given to UK air strikes against Isis in neighbouring Iraq, but on Friday a freedom of information request by the campaign group Reprieve revealed that UK pilots, embedded with coalition forces, had taken parts in missions over Syria.

The defence secretary, Michael Fallon, has been asked to appear before parliament on Monday to explain why these missions were allowed to go ahead without the permission of MPs.

Cameron and Fallon have made it clear they are considering extending the military air campaign to Syria in the wake of the Tunisian beach massacre on 26 June, which claimed 30 British victims among the 38 dead.

They have indicated that they will seek MPs’ approval for an extension of air strikes into Syria, but no vote is expected before the autumn. Labour’s interim leader, Harriet Harman, was last week invited to attend a National Security Council briefing, a move that was interpreted as bid to secure the party’s support in a parliamentary vote to extend air strikes.

In a speech on Monday, which will set out the government’s strategy for tackling the threat from fundamentalist terrorism for the next five years, the prime minister will warn British would-be jihadists that they would not be “some valued member of a movement”.

“If you are a boy, they will brainwash you, strap bombs to your body and blow you up,” Cameron will say. “If you are a girl, they will enslave and abuse you. That is the sick and brutal reality of Isil. We must de-glamourise the extremist cause, especially Isil. This isn’t a pioneering movement, it is vicious, brutal, fundamentally abhorrent.”

The Counter-Terrorism and Security Act, which gained royal assent in February, has put local authorities, prisons, NHS trusts and schools under a statutory duty to prevent extremist radicalisation taking place within their walls.

Cameron will call for an end to “ludicrous conspiracy theories” of the extremists. “The world is not conspiring against Islam; the security services aren’t behind terrorist attacks; our new Prevent duty for schools is not about criminalising or spying on Muslim children,” he will say.

“This is paranoia in the extreme. In fact that duty will empower parents and teachers to protect children from all forms of extremism – whether Islamist or neo-Nazi.”

The prime minister will appeal to a sense of national pride, saying the British respect democracy and the rule of law. “We believe in freedom of speech, freedom of worship, equal rights regardless of race, sex, sexuality or faith. We believe in respecting different faiths but also expecting those faiths to support the British way of life.



“Whether you are Muslim, Hindu, Jewish, Christian or Sikh, whether you were born here or born abroad, we can all feel part of this country – and we must all now come together and stand up for our values with confidence and pride.”