Jahan Mahmood doesn’t bring out his stash of unexploded shells straight away. That part – and to be clear, his ordnance collection is strictly deactivated – comes later on in the evening.

We’re in a community centre in Sparkbrook, Birmingham, the heating’s on the blink and the group is less than half the size it was supposed to be – because of me. Mahmood is giving a counter-extremism talk – a presentation that, he says, has previously put young men off going to fight in Syria – but many of the agreed attendees cancelled at the last minute. Among young Muslims in this community, with its heavy surveillance and Syria-related terror raids, mistrust is running high: the worry is that if you talk about such issues in front of a journalist, the next thing you know, you’re on a watch list.

This evening, half a dozen young men in their 20s are listening, captivated, as Mahmood, a military history researcher, shows them a series of images depicting Muslim fighters on the British side during the two world wars. There is a picture of Khudadad Khan, from what is now Pakistan, the first Indian Army recipient of the Victoria Cross – he single-handedly manned a machine gun post in Belgium in 1914 long enough for reinforcements to arrive, preventing a German breakthrough that might have led to attacks on the UK. Mahmood notes the significance of people who were subjugated by the British empire, joining the fight for British freedoms. Next there’s a slide of a graveyard in Italy full of young Muslim boys from Pakistan who died fighting the Nazis during the second world war; Punjabi Muslims formed the largest component of the British army outside of the UK in both world wars. And there is a photo of King George V wearing a Muslim turban – he had a close relationship with the Muslim military elite – taken during the first world war. “If the EDL [English Defence League] saw this, they’d have a heart attack!” jokes Mahmood.

Khudadad Khan, the Muslim soldier who won the Victoria Cross after fighting for Britain with the Indian Army in the first world war. Photograph: Popperfoto/Getty Images

This work isn’t part of any government counter-radicalisation programme – because, Mahmood says, if it were, it would have no credibility or impact. The UK’s counter-terror programme, Prevent, has been so widely criticised that the terror watchdog recently called for an independent review, citing concern that the policy is counterproductive, causing fear and mistrust. Rolled out by the then Labour government following the London bombings in 2005, the £40m-a-year programme is now known as “MI5 Islam”, so prevalent is the feeling that it is a programme of surveillance on Muslims. Last summer, with some 800 Britons having gone to Iraq and Syria to fight with the Islamic State, the government introduced a legal requirement for public bodies – schools, hospitals and universities – to detect “signs of radicalisation”. In the past four years, 1,424 children between the ages of 11 and 15 have been referred to Channel, the government’s de-radicalisation programme, along with 415 aged 10 and under. The youngest to be referred was a three-year-old. Last week, a nursery in Luton tried to refer a four-year-old to Channel after he drew a picture of his dad chopping up a cucumber and apparently pronounced it as “cooker bomb”.

Back in Birmingham, Mahmood is in his element, talking about Punjabi tribes and Muslim warriors from areas in Rawalpindi and Jhelum, now in Pakistan – where a few of these young men have roots. Some of them haven’t heard this history before; all of them warm to him and to the subject at once. “People always say we don’t fight for freedoms, that we don’t defend the country,” he explains during his talk. “But there we were, doing that.” Later he tells me that this foregrounding of a positive narrative is intended to make potentially alienated young Muslims feel like stakeholders in Britain “so that they don’t end up feeling inferior, or see reason to find an attachment elsewhere”.

It’s just one prong of his counter-extremism talk. He moves on to the present day: the post-9/11 climate of Islamophobia; the wars in Afghanistan and Iraq; the occupied Palestinian territories; the hypocrisy of British arms deals with Saudi Arabia. From there he raises the idea that sometimes, amid “legitimate questions” about British foreign policy, a minority start thinking “that they have to get involved”. And it’s at this point, while he talks about the value of engagement with British society, that the ordnance comes out. It’s a collection of deactivated tank shells, inert aerial shells, sniper bullets and a reproduction land mine – items Mahmood assembled from military memorabilia fairs around the UK. After talking us through their gory effects – a million miles away from any lionised images young men might have of Call of Duty-style, rifle-fighter bravado, or of clean, single-bullet, heroic deaths in combat – he pulls out an amputation saw. We all wince. He also shows us pictures of a fighter with a leg, an arm and a chunk of his stomach missing. Stressing the unsanitary, makeshift conditions on the jihadi battlegrounds of Syria, Mahmood delivers a precision-targeted line: “If you don’t trust people in your own neighbourhood, why would you want to go and trust people you don’t know, fight with people thousands of miles away?”

‘It frightened the hell out of them’ … the collection of mortar shells, bullets and an amputation saw that Jahan Mahmood uses to show the reality of armed combat. Photograph: Christopher Thomond/The Guardian

Mahmood says that in at least one instance that he knows of, this gruesome display turned someone on the verge of travelling to Syria against the idea. He also trains other counter-radicalisation workers in this method. One of them, a youth worker in Birmingham, who doesn’t want to be named, told me that this is the bit that put off three teenagers who had been making plans to go and fight. “It frightened the hell out of them,” he said. “It just stopped them in their tracks. They told me that, had they not found out about this, they could have been duped into going over.”

Mahmood, who used to consult as a counter-terror adviser to the Home Office, now does training courses for councils. But the actual counter-extremism work he does on the ground is all on a voluntary basis, raising resources from the local community. “I can’t take government funding, because I would find myself compromised,” he says. He got started by running a project with street gangs in the area, trying to steer them off drugs and violence – and sees the counter-extremism work he does now as an extension of that, “safeguarding and keeping young men out of trouble”. He says that, in 13 years of counter-extremism work, “nobody on my watch has ever been convicted of terrorism”. He also adds: “I know lots of people doing this kind of work, but they don’t get recognised.” There’s a reluctance to talk about such efforts, for fear that doing so would be misconstrued by the media, or portrayed in a negative light, resulting in disengagement among the at-risk people such projects are intended to reach. But not talking about it might be helping to ferment the misconception that Muslims across the country are somehow not doing enough to tackle extremism: prime minister David Cameron has several times urged Muslim communities to “do more”.

Najam Sheikh, 41, a business consultant and father of three, works on counter-extremism in Dewsbury as part of a community group called Engage, which was set up last year. Talking to me about Prevent, he says: “From a community point of view, it’s an Islamophobic, toxic policy that claims to be working towards deradicalisation but is targeting the community and de-Islamising Islam,” he says. Even purely in counter-extremism terms, says Sheikh, the research suggests this would be a bad thing: people with a solid grounding in religion aren’t the ones who turn to terror. He says he cannot support Prevent’s agenda, or take its funds. “If I said I worked for Prevent, I’d be called a spy, an informant and a government stooge,” he says. “The barriers would come up and the doors would close.”

Hassan Munshi (left) and Talha Asmal, who left Dewsbury for Syria to join the Islamic State. Asmal blew himself up in Iraq, becoming Britain’s youngest suicide bomber. Photograph: PA

Dewsbury, in West Yorkshire, hit the headlines last year as the home of Britain’s youngest suicide bomber, Talha Asmal, who was groomed online and blew himself up near an oil refinery in Baiji, Iraq. Hassan Munshi, 17, also travelled with Asmal to join Isis and is thought to be in Syria. Munshi is the brother of Hammad who, at 18, became Britain’s youngest convicted terrorist in 2008. In shock, living in one of the most deprived parts of the country, facing an onslaught from the far-right and feeling neglected by local authorities, this community got behind Engage, funding and volunteering to keep it going. Part of its work has been to reintegrate 14 young men who were friends of Asmal and Munshi and classed as radicalised (they have all since been through the government Channel programme, and six at one point had their passports removed). “Some of these boys were ready to go, believe me,” says Sheikh. “They were shunned for being involved, but where everyone was pushing them away, we tried to bring them closer.” That involved talks, meals, activities such as a football tournament, and taking them to see Islamic scholars “to give them a correct narrative, to show them how that narrative was twisted”.

Working with other young, potentially vulnerable people in the area, Sheikh explains the approach: “We can’t do it in a direct way, so we try and provide diversionary activities,” he says. “We take them go-karting, or for a meal, give one-to-one mentoring, or help with a CV. In the process, we also tell them: look, this is what you don’t do, this is what you avoid on social media.” As he describes it, this counter-extremism work is, at its core, about pastoral care and contact with positive role models. “Our worst case scenario is any person from our community who ups and leaves to go to Syria and join the animals that are Isis. We don’t want any more parents to go through that.”

Another community-led project, Media Cultured, in Middlesborough, is focused more on school children. As its director, Amjad Khazir, 37, explains, some of the organisation’s aims run parallel to Prevent, though it is not funded by the programme because “people would turn off”. Media Cultured provides schools with resources and strategies around building cohesion and countering extremism. For educators, given the unwelcome task of monitoring their students for signs of radicalisation, says Khazir, “the sense of relief on their faces when we come in is palpable”.

‘If the EDL saw this, they’d have a heart attack!’ … King George V wearing a Muslim turban during the first world war. Photograph: Print Collector/Getty Images

One of the men Mahmood has helped in Birmingham is Sabeel, now 26 and a new father. When Mahmood met him, Sabeel was an alienated teen, part of a gang, playing along with them joking at the news of the murder of Ken Bigley in 2004, a British contractor taken hostage by an extremist terror group in Iraq. “I was born in this country, but I was getting racist remarks, and when you’re told to go back to your own country, it obviously doesn’t make you feel part of society,” he says. After meeting Jahan and attending his talks, he turned right around, and started to feel proud of his identity as a British Muslim. “Going from a hardline street boy to what I am today – if it can change me, it can change anyone,” he says. Sabeel has been helping Mahmood ever since, bringing other, potentially vulnerable people to his talks. Word of mouth is mostly how it works – as we leave Mahmood’s talk in Sparkbrook that evening, one of the other attendees, who knows Sabeel, says he wishes he had come along years ago.

Sabeel says he is changing people’s minds in conversations, and countering arguments in everyday life. “Foreign policy is very big in young people’s communities,” he says. “And when they don’t feel part of society and they’re always getting slandered for being Muslim, it makes them angry. If they haven’t got the right people and the right support around them, they might go and do stupid things.” Such engagement with foreign policy issues – which Mahmood also does in his talks – is in contrast to the government’s counter-radicalisation policy, Prevent, which classes concern about British policy in the Middle East as one of the potential signs of extremism.

When I next speak with Mahmood, he is busy packing his inert ordnance kit away to take to another counter-terror training talk, one of many he does across the UK. “This has become an important part of who I am,” he says. “I do it because I have to do it. I do it because I’ve seen the results. When people tell you that you’ve stopped them going to a war zone, made them want to stay home and help the local community – you know you have to keep doing what you’re doing.”