The writer-director’s four-parter could serve as an eloquent anti-recruitment video for Isis’s death cult, but ultimately didn’t get us into the mindset of his protagonists

In The State (Channel 4), Shakira Boothe is watching her son Isaac happily playing football with his new mates. Then she notices something – the ball was a human head.

This, it turns out, is an Islamic State training camp, and Isaac, who will turn 10 in two weeks, is being toughened up for battle. Shakira (the superb Ony Uhiara) summons him for a telling off. “Hurry up, you’re embarrassing me,” snarls Nana Agyeman-Bediako as Isaac, before scampering back to the kickabout.

It is a psychologically incisive moment from writer-director Peter Kosminsky, in which maternal authority is trumped by the testosterone thrill and comradeship of Isis’s death cult.

It was then that Shakira realises she has to get herself and Isaac home, even if home is the decadent England she left months earlier – that is, if she wants to stop her kid becoming a pre-teen martyr for a cause in which she scarcely believes any more.

Ever since Chris Morris’s satirical 2010 film Four Lions portrayed homegrown Islamist terrorists as Pythonesque clowns, mystified apostates like me have yearned for a more convincing account of why Brits turn jihadist. But Kosminsky’s drama, broadcast over four successive nights this week, doesn’t come up with answers.

The real charge against The State is not the unfair one that it risks justifying extremism (if anything, it could serve as an eloquent anti-recruitment video). Rather, it’s that Kosminsky fails to make us empathise with his three Brit protagonists or really understand why they chose Isis. That’s a particular shame because with earlier TV dramas such as The Promise and Wolf Hall, he’s been so effective at getting us into his protagonists’ mindsets.

Instead, Kosminsky goes for the easier option of showing us how protagonists are stripped of their delusions in a harrowing, protracted dance of the seven veils. But, at least for me, that drama of disillusionment is unsatisfying. Each mortified reaction shot at some horror – beheadings, Shakira being asked to harvest kidneys from wounded enemy troops, the football head – is premised on these Brit jihadists having been unconvincingly ignorant about what Isis involved before arriving in Raqqa. But how could they have thrown in their lot with a cause about which they, evidently, knew so little?

And yet, despite this shortcoming, The State is compelling and deranging. There is even space for grim comedy when Ushna Kaleel (Shavani Cameron) downloads an app to translate her (surprisingly sweet) Isis fighter husband’s spoken Arabic into written English. After she serves him dinner, Kaleel looks excitedly to her phone for the translation of his first message. Up pops the disappointing result: You can’t cook.

Most compelling of the three narratives is that of Jalal Hossein (Sam Otto), a young man from Wembley in Syria for jihad, but also to find out whether his Isis-supporting brother died martyr or coward. The truth, we discovered last night, is more complicated: his brother was executed, like other Isis comrades, for refusing to fight anti-Assad rebels, many of whom were their friends. Kosminsky doesn’t have airtime to dramatise Syria’s manifold geopolitical miseries in detail, but in such moments nods eloquently towards the horrible nuances of Middle East politics his Brit jihadists failed to comprehend before they arrived.

I love the scene in which Hossein’s dad arrives to convince his errant son to come home. Echoing Hanif Kureishi’s My Son the Fanatic, Kosminsky’s writing here pits paternal fury that his boy didn’t understand Islam nor appreciate what Britain had given to his exiled parents against exasperating youthful self-righteousness. “This is pointless,” the youngster tells his dad. “End of.”

But it isn’t end of. Like Boothe, Hossein is painfully disabused of his Islamist ardour.

Earlier, he bought, for $200, a woman and daughter at a slave market where the spouses of defeated enemy troops were sold. Revolted by the idea of doing what his comrades customarily do, namely (as one fellow jihadist chillingly put it) raping their female captives into Islam, Hossein treats these violated women with compassion, finally deciding the right thing to do was to free mother and daughter at the Turkish border.

But at the border, his plan went wrong. The women are captured by his Isis comrades and summarily shot, while he is dragged off, possibly to face execution for his betrayal. Still, I can’t help admire him for finally resisting the misogyny of Isis and for trying to do the right thing.

Unlike him, Boothe manages to escape. After fleeing Syria, she and her son arrive by refugee boat at a European beach. Later, at the British border, she is stopped by a counter-terrorism officer, understandably sceptical when she says she wanted to publicly recant her jihadist beliefs in order to dissuade other Brits from joining Isis. He is worried she and her son might actually be a sleeper cell bringing jihad back home. Kosminsky is on the money in exploring that thought: as Isis loses Raqqa, Sirte and Mosul, its best hope may be to take the fight to the apostate west by deploying brainwashed kids.

The counter-terrorism guy has another idea – Boothe should spy on Britain’s radical Islamist community for him. “I can promise you it’ll be more effective than writing an article for the Guardian,” he says. Bloody cheek.

At the end of the drama, what she will do remains uncertain, but what the counter-terrorism officer thinks of her is very clear. “You haven’t exactly been a good mother, have you?” he asks. Fair point: good parents don’t take their nine-year-olds to Raqqa to be trained as martyrs, generally. And yet, despite everything, it’s a measure of how sympathetically Uhiara plays this foolish, misguided woman that, as she struggles with tears and self-disgust in response to that question, I feel a little sorry for her.

• The State is airing in Australia on National Geographic, on Foxtel