Peter Kosminsky: People will say I have made a recruiting film for al-Qa'ida

Muslims are furious, says Bafta-winning writer and director Peter Kosminsky, whose new film features a suicide bomber. But what would he know about that?

What the hell would you know about being a suicide bomber? That is the question that keeps on coming to mind as Peter Kosminsky attempts to explain why someone would blow themselves up in the name of Allah. "British Muslims are fantastically angry and disillusioned," he says. "They are infuriated by a foreign policy that appears to be an attack on Muslims worldwide – a new Crusade – and a shockingly large series of security measures which seem to be aimed solely at them."

The man saying these words is white, Jewish, privately educated and in his fifties. He is drinking tea at his beautiful cottage in the Wiltshire countryside. Yet he is trying to describe how a young, moderate medical student from Leeds could become so outraged by what is happening around her that she is willing to strap on explosives.

Nasima is fictional, but Kosminsky insists her motives are fact. Her story is told in his new film Britz, which will be shown on Wednesday and Thursday to mark Channel 4's 25th anniversary. The channel is clearly trying to show it can still make radical drama, and Britz is sure to attract old-style fury. "I know a lot of people will be very, very angry," admits Kosminsky. "I've no doubt somebody will accuse me of making an al-Qa'ida recruitment video. That's the risk you run if you try to understand what's going on."

Others will surely object to Muslims being shown as extremists yet again. Sohail, the lead character in the first of the film's two parts, is recruited by MI5 and joins a team trying to stop a potentially devastating attack on Canary Wharf. Nasima, his sister, the trainee doctor whose story is told in part two, is enraged by the house arrest and suicide of her best friend and despairs of impotent political protest. Both are all-or-nothing characters who pour scorn on those trying to take a middle path. "I'm being intentionally provocative," says the writer and director. "It's what I do."

It sure is. His last film The Government Inspector was an account of the death of Dr David Kelly. It won him a Bafta and was one of the few real blows landed on the Blair administration over its attempt to justify the invasion of Iraq. Britz tries to keep up the pressure.

"There has been a real failure to engage with what it feels like to be one of the 1.6 million Muslims living in Britain today," says Kosminsky, before concentrating on the few who chose to blow themselves up on the Tube. "We have to understand how intelligent fellow Britons could be so alienated, so frustrated and so furious that they could take what appears to be an insane and immoral step. Otherwise how can we ever hope to prevent it happening again?"

Fierce in his assault on Tony Blair, Kosminsky sees no reason to relent now that there is a new Prime Minister. "You couldn't get a paper between them politically; they just happen to detest each other. Gordon Brown would like 90-day detention without trial on the statute books as soon as possible. The raft of recent legislation that has so alienated young Muslims will continue."

But really (that question again) how would he know anything about that alienation? Kosminsky lives in a quiet village, in an old house with a crab apple tree and a sundial outside the window. His children go to boarding school. His neighbours are almost all white. How can someone like him possibly get inside the heads of a young Muslim man and woman growing up in Yorkshire? What right does he have to try? "That is a question that crosses your mind every time you do something," he says with a smile.

Kosminsky is a slender man, with thinning black hair, who is dressed in pale jeans, a white T-shirt and a fleece. Since he is a Fellow of the Royal Television Society, let's describe him in TV terms: the look of a slimmed-down Tony Robinson, the voice of Rowan Atkinson. He speaks softly but precisely. He is self-deprecating, but takes his job very seriously. And here in his own book-lined room he is prepared to be frank.

"When I made Warriors for the BBC [about peace-keeping in Bosnia], I had never been a soldier. I've never made a film about a subject I knew a lot about beforehand." That may seem like a startling admission, but Kosminsky believes it gives him an advantage.

"I always thought I was of more use to the audience starting from a position of educated ignorance. I don't have detailed knowledge of being Muslim in Britain – but I have the wherewithal to gather that knowledge." That meant commissioning a team of researchers led by Ali Nausahi, a second generation immigrant from Bradford, to interview British Muslims aged between 18 and 35. The majority of the cast and many of the crew were of the same faith or background.

"The level of fury that came out of the research was astonishing," says Kosminsky. "It scared me because we are sitting on a time bomb. These are highly intelligent, able people who are very angry with our society and have the means to do something about it."

Some of the anger comes from Ummah, the strong Islamic collective sense that connects Muslims across the world. "It's not something they pay lip service to. It's central to their faith."

Some of it was caused by the relentless petty ignorance and hostility of the authorities, as shown in the film – such as the police officer who slams an innocent man up against a wall and calls him a "Paki fuck", or the armed raid whose only haul is six wholesale packets of black pepper. "Those scenes are anecdotes lifted straight from the research," says Kosminsky. "I didn't make them up."

The message of Britz is that people get pushed towards radical action by a mix of ideology and emotion and the accumulated effects of the smaller decisions they make. "We don't do any kind of service to the friends and relatives and survivors by simply regarding the 7/7 bombers as a group of mindless bigots or insane people who are doing it because they genuinely believe they will spend eternity being embraced by 27 virgins," insists Kosminsky. "Mohammad Sidique Khan [leader of the London bombers] was teased for loving everything American. He used to go round in a cowboy hat."

But doesn't dwelling on the terrorists distort the picture of 1.6 million peace-loving Muslims in the UK? "I think that is valid. I would say, though, that when we were auditioning Muslim actors they kept saying, 'At last, somebody is writing about us as they really are.'" They would though, wouldn't they? This is glossy, landmark drama. They wanted the work. "Yes, but is is also the desperation of people who usually only see themselves portrayed as two-dimensional characters."

Wouldn't it be better, then, if Muslims had the chance to tell their own stories? "Who's listening?" That sounds brutal, but he means to be realistic. "The truth is that I've got the platform. I also do believe that in some ways an outsider can speak with more authority. That way there doesn't appear to be any special pleading."

Unlikely as it seems, there are also some ways in which Peter Kosminsky feels a personal link with the people he portrays in Britz. "I am the child of immigrants," he says. "I have felt that tug of loyalties throughout my life."

His father was born in the East End of London, to a Polish family that had fled the pogroms. His mother came to Britain as an unaccompanied refugee from the Nazis on the Kindertransport from Vienna. Her suitcase was lost. "She arrived at Victoria station at the age of nine, not speaking any English, with a label around her neck and without any possessions but the clothes she was in."

His parents made every effort to become assimilated. "All my father wanted was to assume the trappings of the country that had taken his family in. I got a lot of Sohail from my father." Peter went to Haberdashers' Aske's public school, then on to Oxford University. "I still feel the battle inside. I had this almost visceral desire to dig in to the host society – but part of me was ashamed of that."

A BBC traineeship led to a distinguished career in documentary making. Kosminsky has also directed Hollywood films, including an adaptation of Wuthering Heights starring Juliette Binoche, but in recent years has become best known for docu-dramas attacking the Labour Government. "The Project was written from the point of view of somebody who had been very excited at the arrival of New Labour and felt horribly let down and disappointed," he says of the 2002 film. The next he wrote himself. "The Government Inspector was about how we went to the war, and the deception that was perpetrated. Britz is about one aspect of the social consequences of that."

Astonishingly, the secret services agreed to talk to him. Kosminsky felt flattered to be inside Thames House, the ultra-high security home of MI5. "They were incredibly helpful. Of course, then you feel honour-bound to depict them reasonably." Were the spooks trying to win over one of their loudest critics? "I think that's part of it. But being a wily old fox you're alert to that. It's part of the reason one works in a team."

Of course Britz is just another film, on one level. Peter Kosminsky is just another successful writer and director, sitting in his country idyll making up stories about lives he will never have to share. But to his credit, he is aware that for the MI5 agents, for Muslims of all persuasions, for the families and survivors of those who died in previous terrorist attacks, the stakes are far higher. And of course, writers and film-makers have have been threatened with violence and death for far less forceful statements than this. "Who wants to play safe?" says Kosminsky with a grin. "I am incredibly lucky. I am one of a handful of people who gets the artistic freedom and the resources. I have an absolute bloody obligation not to squander that."

Further reading: 'The Islamist: Why I Joined Radical Islam in Britain, What I Saw Inside and Why I Left', by Ed Husain, (Penguin, £8.99)