'People are having an identity crisis'

His parents led prayer meetings, reading classical Islamic verse and their own spiritually inspired poetry. This created a tension in Cosh's life; he had a deep, textured understanding of his parents' faith, while being exposed to the freedoms and excesses of youth in a big city.

"The truth is that when you're brought up within an ethnic minority, you don't feel British and you don't feel Turkish, and when you go to Cyprus you're made to feel a foreigner.

Here you're a bloody foreigner, and at the same time, you don't agree with what your parents teach you to do, so you go out and do what society teaches you to do.

And you don't agree with that, because it's bloody boring - I was good at getting drunk and getting laid. I was going to clubs every night. I got to a point where I thought, 'Is this it?' I believe there is a God, and I started looking for a connection between me and that God."

Islamic extremism managed to create order out of a convoluted life experience. His early childhood was spent in Tottenham; at the age of 10, his family moved to Palmer's Green, where they live today. Cosh's closest childhood friend was a Greek Cypriot, as is his current best friend.

Relations between Turkish and Greek Cypriots are warm but complicated: "There is always political friction, but this is one community. We shop from one another's shops and go to one another's weddings." Intermarriage, however, is a problem: "That's when it kicks off."

In The Battle of Green Lanes, Cosh also plays the lead character, Erol, who finds a clear solution to the exhausting, everyday chafing between London's Turks and Greeks in radical Islam, a colour-blind creed that transcends national differences.

In his writing, Cosh has not shied away from the racial differences that his characters see - referring casually to a London full of "pakis", "coons" and "bubbles". The adjectival use of foul language is constant, plausible and comedic.

But, Cosh says, "the play is not just about a foreign kid in north London with an identity problem - it's bigger than that. What we went through, being in this new place, the whole world is now going through because of globalisation. People everywhere are having an identity crisis."

This, he believes, is the nub of radical Islam's appeal - to him, and to young men like him - because it presents a strong ideology. He describes the people at the meetings he attended as having "a strength in them I hadn't yet gained. Their social conscience and political awareness impressed me. They had strong opinions on a wide variety of issues.

"Islam is a political, social and economic system," he adds, one that has taken the place vacated by communism as the ideological alternative to capitalism. "What impressed me was the sincerity of these people, who wanted to make the world a better place."

Cosh wrote the play 10 years ago, after endless auditions for parts as kebab-shop owners. Though he has had some success in The Bill and other TV dramas, "I was always being cast as a foreigner," he says.

"So I thought I might as well write a part, cast myself and tell the real story." It was originally a four-hour screenplay that met with incredulity from agents. Four years ago, he adapted it for the stage; but it was not until a year after 9/11, when he presented it to Kerry Michael (artistic director of the Theatre Royal) that its staging looked likely.

Eventually, Cosh's dramatic ambitions led to his departure in the mid-Nineties from Hizb ut-Tahrir, after it insisted that he had to give up acting. Through his own reading, too, he had also grown to question their position on many issues, especially on the history of modern Turkey. Ataturk, who founded the secular state, is believed by them to have hell balanced on his shoulders.

If it was intolerance, finally, that turned Cosh away from radical Islam, there is perhaps some contradiction in the intolerance that his play shows towards homosexuality but does not resolve.

A Greek Cypriot, Tom, is in love with Erol but cannot declare it in the macho environment in which they operate. It is possible that Erol, though presented as a smooth guy with an eye for the girls, is tempted by his friend's coy advances and that fear of his attraction leads him to the extremist meetings.

Fundamentalism, Cosh says, solves some problems by ignoring them. Its attitude towards homosexuality, though, is clear. In one scene it is stated that, "Islam teaches us that [gays] should be taken to the highest point in the land and thrown off".

"We have had nights in the theatre when that line gets an ovation," Cosh says. "It made me feel sick. But for it to be scary, you have to be able to see some power in their argument."

Married and a father of two, Cosh's life is now a largely secular one divorced from extremism; he does retain an Islamic sensibility, and abstains from alcohol during Ramadan.

He wants to make people think and open a dialogue: "With the extremists on both sides, people are not going to be allowed to find common ground," he says. "People are going to be pushed into their fighting corners. It's the game of politics, and humanity doesn't always play a part in politics."

The Battle of Green Lanes is at the Theatre Royal, Stratford East (020 8534 0310) until 13 November.