KADIZA Sultana, one of the three London schoolgirls who fled to Syria last year, was said to have been disillusioned with life in Isis territory when she was reportedly killed by a Russian airstrike. Kadiza, who was just 16 when she and her friends Shamima Begum and Amira Abase left their Bethnal Green homes, had been radicalised and groomed online into believing that life under Isis would be some kind of religious utopia. Instead it led to an early death.

One 13-year-old girl from Birmingham, who was identified under the UK Government's counter-terrorism programme, Prevent, told an intervention worker she thought life under Isis would be an “Islamic Disneyland”. Luckily for her, she never got out of the UK. The authorities prevented her from travelling to Syria and she is now back at school, grateful to have seen the error of her ways.

In contrast, Asqa Mahmood, who left Glasgow in 2013 to join Isis, has gained a notorious reputation as one of the country’s most violent jihadi brides. Alleged to have encouraged other British women and girls to travel to this caliphate, she has glorified the deaths of British citizens in last summer's Tunisia massacre. What was particularly noticeable about Aqsa, a keen Coldplay fan and Harry Potter enthusiast, was how her identity converted into "Umm Layth". With this new name, she had transformed into someone else – unrecognisable by even her own parents, who have described her words as "twisted and evil".

What turned this lover of Disney films and Harry Potter into one of the UK’s most violent jihadi brides? What convinced Kadiza, a promising A-grade student, to give up everything for a barbaric death cult?

There is no definitive profile of those drawn to terror, but there is little doubt that Aqsa, like many other female Isis supporters, bought into what I call the Salafi-Islamist worldview. Different to Islam, this modern 20th-century ideology is a fusion of Islamist and Salafist beliefs. Islamism advocates the idea that Muslims are required to establish and live in a single global caliphate which will be governed by a totalitarian interpretation of Sharia law. Salafism promotes a blind and puritanical literalism which aspires to an Islam practised by the early Muslims. Both movements conflict with human rights and struggle with modernity, and when fused, the result is a political-puritanical ideology that is alien to traditional Islam, yet promotes itself as “normative” (or "orthodox") Islam.

Salafi-Islamism has become hugely influential, largely because of the rise of social media, which is fully exploited by groups like Isis. We may hold little sympathy for Aqsa or Kadiza; but the truth is they are victims of Salafi-Islamism.

The radicalisation of these young women may happened online, but the promotion of Islamist ideology was happening before the advent of social media. Indeed, it has been openly preached for decades by preachers and organisations in the UK,and from the 1990s onwards, thousands of Muslims attended Salafi and Islamist events.

A central theme to this ideology is the notion that the West is at war with Islam and Islam is at war with the West; and that Muslims should strive to live in Dar al Islam, or the land of Islam, as opposed to Dar al Kufr, the land of disbelief of which Britain is allegedly part. There is no middle ground.

This extreme, anti-Western worldview is shared not only by violent extremist groups like Isis, but also by global political organisations such as like Hizb ut Tahrir (the "party of liberation"), whose UK branch reviles at the very notion of a British Islam. The idea of a reconciled British Muslim identity clashes with the binary Islamist worldview and the narrative of a caliphate.

What we have not often appreciated is that Islamism – whether of the violent or non-violent variety – forces a choice between British and Islamic values. Young British Muslims are told by Islamist preachers that they have to choose one over the other. In 2006, the proscribed Al Ghurabaa, a spin-off organisation of the banned Al-Muhajiroun led by the now convicted Anjem Choudary, plastered bright rectangular yellow stickers over East London, which absurdly stated that while Islamic values consisted of “worshipping Allah, honesty, charity, family values and morality”, British values included “state terrorism, exploitation, homosexuality, alcohol, gambling”. This dishonest propaganda fails to acknowledge that these Islamic values are not just limited to Muslims; indeed many Britons would argue that charity and family values are their values too. Equally the idea that some Muslims do not drink alcohol or engage in gambling is a deliberate cover-up of the truth and a cynical attempt to promote Muslim supremacism and hatred of non-Muslims.

But for many young Muslims struggling with their identity in a post 9/11 world, this black and white view is appealing. For the first generation of immigrant Muslims, ethnicity rather than religion was the more prominent identity marker. In contrast, second-generation British Muslims, influenced by the rise of global Islamic and Islamist movements, began to define themselves in terms of their religion. Influenced by revivalist puritanical Muslim groups, some second and third-generation British Muslims sought what they perceived to be a "pure" interpretation of Islam, free from what they believed were the corrupting influences of their parents’ culture. This allegedly "authentic" interpretation of Islam was often packaged in the form of Salafi-Islamism and has been widely propagated in the UK.

We cannot underestimate the relationship between Islamist ideology, identity and anti-Western sentiment. Leila, a female intervention caseworker I interviewed for my book, The Battle For British Islam, used to be part of the extremist organisation Hizb Ut Tahrir. She sees how ideology, identity and anti-Western sentiment repeatedly rear their heads among the pro-Isis women and girls she works with. She has worked directly with around 25 women and girls who have been radicalised by Islamist extremists, each and every one whom professed anti-British and anti-Western sentiments.

Journalist Nabeelah Jaffer, who spent months talking to British and American jihadi brides, found that all the women she talked to held a fundamentalist understanding of Islam, and that it “lay in whatever appeared to be as anti-Western as possible … Opposing the West was their measure of religious authenticity”. So conflicted were these women, they sought to eradicate their Western identities. Being Muslim and British could not be compatible in their eyes.

Studies on radicalisation have found identity to stand at the fore of the radicalisation process.

Research shows that around a quarter of all terrorist convictions from 2001-2014 involved religious converts, despite only three or four per cent of the British Muslim population are converts. Because converting often involves fundamentally altering their whole way of life, these people can be extremely vulnerable to extremist propaganda.

While it is true people who feel a lack of belonging are often more vulnerable to Islamist extreme propaganda, this ideology can also impact on one’s sense of identity and belonging. To put it another way, those who confidently accept their Western identity and don't see it conflicting with their faith, are less likely to find the anti-Western rhetoric of Islamism appealing.

Countering the Islamist threat is no small feat. For it to be overcome, we need to recognise the important role that our society and institutions, including faith leaders and mosques, can play. The long-term problem of Mosques unable to make themselves relevant to young people, has weakened our defences against Isis's aggressive propaganda machine. As a result, young Muslims prefer the mosque of YouTube, full of charismatic extremist preachers brandishing their hate, to the bricks and mortar of their local mosque, where sometimes the imam can't even communicate in English. This must change and it must change now.

In particular, mosques need to reach out to women and girls. Too many mosques are unwelcoming to females. Earlier this year, Glasgow Central Mosque found itself severely criticised for not having a single woman sit on the committee. The lack of inclusion of women and fit-for-purpose teaching for girls, can only make them vulnerable to extremist ideology as they seek religious guidance online where unfortunately preying radicalisers are waiting for them. Aqsa Mahmood herself became radicalised online, after being hooked by the speeches of a male Australian extremist preacher.

Glasgow Central Mosque again found itself under the spotlight when one of its imams praised an extremist for the 2011 murder of the Pakistani politician Salman Taseer, who had campaigned for the reform of the country’s blasphemy laws. In the battle against extremism this serves to undermine the efforts of British Muslims and the local community. As many Muslim mothers have told me over the years, they and their children deserve better. Muslim congregations can and must take a pro-active stance in holding their religious leadership accountable. They need to challenge and speak out against those who promote hatred, violence or discrimination. Demanding better leaders has never been more critical for our children’s wellbeing, and for the whole of our society. Extremism spreads fear, suspicion and as a result undermines our cohesive and shared communities. Our faith leaders must take the lead in engaging with young people and women, creating a culture of respect, inclusion and tolerance.

Secondly, schools can play a leading role in promoting equality and human rights. Islamist extremism – or indeed any form of extremism including that of the far-right – are in direct opposition to human rights and respect for other religions. Teaching these values to our children and encouraging them to champion equality from an early stage helps build resilience against extremist narratives. The ability to think critically is a skill all children need to be taught, whether in our schools, madrassas or Sunday schools; in an era of social media where one can find their own views being reinforced through an echo chamber effect, it is vital that children are taught not what to think but how to think and to question what they are reading.

Thirdly we must all speak out against those who help the Islamist narrative by suggesting that Muslims do not belong here and who promote wider anti-Muslim bigotry. This only serves the cause of Islamist extremists who seek to divide us as a society and who try to promote the West as the enemy. Young Muslims must feel that they are not viewed as a suspect community but that they have a stake in our country and that solidarity is always afforded to them by their fellow Scots. In the post-Brexit political climate, it can be easy to focus on differences, rather than the things we all have in common. We must resist the polarisation of our societies and of our common identities.

Finally as I argue in my book, cultivating a British Islam has never been more important. This means an Islam which is rooted in British values, which respects democracy, human rights and equality. It sees no conflict in being British and Muslim or Scottish and Muslim, and rather than dreaming of a caliphate, it recognises Britain as home. A British Islam by default undermines the Islamist worldview; it opposes the notion of wanting to live in some distant so-called caliphate in Syria. There is no doubt however, as hundreds of British Muslims have left the UK for Isis, that the struggle for a British Islam is one we are in the midst of. Islamist inspired radicalisation and terrorism remains one of the biggest challenges facing us in Britain. Isis have repeatedly encouraged radicalised Muslims to carry out attacks in the UK, to kill their fellow Brits. The Battle for British Islam is of utmost importance – and for all our sakes, it is a battle that we must win.

Sara Khan is author of The Battle For British Islam: Reclaiming Muslim Identity From Extremism, co-authored with Tony McMahon. She appears at the Edinburgh International Book Festival this evening at 6:45pm in the Baillie Gifford Main Theatre www.edbookfest.co.uk

Khan is also co-director and co-founder of the counter-extremism and women’s rights organisation, Inspire