When the first schoolgirls ran away to Isis I had some sympathy for them — at least, I could see how they’d been suckered in. The girls were young, daft, desperate for a cause. They’d nosed about online, and found the Twitter feeds of jihadi wives who sell Syria as a teenage paradise: all fast food, deathless love, martyrdom and shopping.

Because I felt for those first schoolgirls, I kept following their progress, checking for them online as they set up in Syria, married, and began to tweet themselves. But as I followed them on social media, my sympathy soon turned to disgust.

‘Happy #9/11’ wrote young Zahra Halane, one of the twins from Manchester who fled to Isis last year. ‘Happiest day of my life. Hopefully more to come. InSha Allah #Is.’

Her sister Salma cheered on the Charlie Hebdo massacre: ‘May Allah protect all the mujahideen in Franceeee!!! Shooting was maaaad!!’

Um Ayoub, 16, also from England, listed a few of her favourite things: ‘Vans, Nike, Chelsea FC, beheading Kafirs.’

It’s strange to feel one’s own heart harden; odd to notice that, without willing it, one’s thoughts have changed. All this dancing on the kafir’s grave had the same effect on me as I expect it had on others. The girls who once seemed victims became aggressors. They want to kill all unbelievers? Their former school pals? Me? Well, let them go to Syria, then. Let them stay there. Why waste money saving kids who want us dead?

It’s a satisfying position, and one I was enjoying right up until last week, when I read a report written by a think tank, the Institute for Strategic Dialogue. ‘Till Martyrdom Do Us Part’, it was called, and it showed me what a terrible dunce I’d been. We must take these girls seriously, said the ISD, and we must stop them leaving — or else we’ll be making a historic, catastrophic mistake.

ISD say our girls are being lured not to Syria but to Libya now. A new cry has gone up on Twitter; the beckoning of British-born brides of Isis to their little sisters back home: ‘Come to Libya. Hijra is not only to Shaam [Syria]. Libya needs you too.’ ‘Life in Libya is mind bogglingly great.’ ‘Make your Visa and go to #IS in Libya. We need to raise more awareness.’ And all over London, daughters who seemed safe in their bedrooms start typing secretly: where should I fly to? How do I find you?

Isis have held territory in Libya for a while now, thanks to Mr Cameron and his idiot war. They run training camps on the coast near the Tunisian border (Jihadi John was a graduate) and have just retaken Sirte, Gaddafi’s old home town. But as ISD say, this sudden call for girls changes the game. Girls mean brides and brides mean babies, brainwashed from birth. Girls mean Isis are ready to secure another state, a new caliphate — and in terms of our security, if not human misery, Libya as a caliphate makes Syria look benign.

Libya is the dream for Isis, the real promised land. There’s oil to be sold and untold zillions to be extorted from migrants hoping to cross the Med, but more importantly, it’s the perfect launch pad for attacks on Europe. One Isis supporter, quoted by the Telegraph’s Ruth Sherlock, put it like this: ‘Libya has a long coast and looks upon the southern crusader states which can be reached with ease by even a rudimentary boat.’

And here’s where our schoolgirls might really make their mark. They’ll get in those rudimentary boats with the refugees, and with their children perhaps for added innocence. They’ll be rescued, make contact with comrades on the ground, then pick their moment to detonate off to paradise, taking the kafir with them. This is Isis’s plan, openly discussed online, to take terror to infidel Europe. The stowaway schoolgirl jihadis of today are tomorrow’s homing missiles.

But don’t Isis say a woman’s place is in the home? Aren’t Isis wives condemned to a life of cookery and beating up their Kurdish slaves? For the moment, yes. There is no lethal brigade of Isis lady assassins, much though the red-tops wish it so. But worshipping violence creates an appetite among the faithful. Beheadings are moreish, as England once knew well, and the longer a girl’s in the caliphate, the more bloodthirsty she’s likely to become. ISD have spotted, they say, a shift in the thinking of jihadi wives, an impatience among women to get to the hacking and torturing themselves. Umm Ubaydah, a western woman in her early twenties who acts as mentor to youngsters overseas, tweeted hopefully: ‘Maybe the time for us to participate is soon?’

Just think, say the ISD, of Chechnya’s female fighters, who first played just a sedate and supportive role in the Russo-Chechen wars. During the second war, after their husbands’ ‘martyrdom’, these homebodies became the ‘black widow’ suicide bombers.

And don’t imagine Isis don’t see the potential in their girls. In return for the release of the Japanese hostage Kenji Goto, they demanded ‘sister’ Sajida Mubarak al-Rishawi, a failed suicide bomber held in Amman. It wasn’t that they wanted her particularly, but demanding a sister sent a message to the rest worldwide: we value you — and especially if you’re prepared for martyrdom.

Each lonely schoolgirl, curious, religious, hormonal, is a godsend to Isis. That’s why they devote so many thousands of hours to converting them, to talking theology on the internet and making friends.

So the mystery of it all turns out to be not why the girls go so much as why we, Britain, do so little about it. No one in government is much concerned, says the ISD, no one thinks runaway teens a big deal. Our spooks and wonks have other concerns, which is why the ISD wrote their report. There’s some talk of educational videos and of learning from the campaigns that stopped kids smoking, but what’s really needed are mentors of our own, legions of them, to counteract Isis’s recruiters. We need to take these girls as seriously as Isis takes them or we really will live to regret it.