Graham Anderson and Joseph Flaherty are two boys like any others. They both love football and play for a youth team called Glasgow City. But certain things mark them apart from each other.

One supports Rangers and the other Celtic; one has a granda who was an Orangeman and wants him to take part in his lodge’s Orange Walk and the other has a granny who remembers the days when building sites displayed signs saying “No Irish need apply” and advertisements for housemaids said “No Catholics”.

Through various twists of fate the boys became friends, united by a love of football and united in helping a Kurdish asylum-seeker who has been badly injured in a brutal attack by a gang of youths.

Although Graham and Joseph could be two lads living and going to school in Glasgow, they’re not. They’re fictitious. They are the main players in the latest novel by the Carnegie Medal winning author Theresa Breslin.

Divided City is her attempt to confront one of the biggest stains on the face of the city: sectarianism. She describes how Graham has to hide his religious background by adopting the name Gregory when he visits Joe’s house, and his reactions to Joe’s “green grotto” of a bedroom, festooned with Celtic paraphernalia.

Between them, the two boys rehearse the arguments so often offered by opposing Catholics and Protestants.

Graham says: “Everybody’s got the right of free assembly, or should have.

That’s why the Orange Walks take place.

“My granda says his people had to fight to keep their religious freedom.

That’s what the Battle of the Boyne was all about. On the twelfth of July in 1690 King Billy won that battle so that everybody could have their own faith and walk where they choose.

“Your people especially shouldn’t object to someone standing up for what they believe.”

Joe replies: “Well, my dad says it was mainly to do with leaders wanting land and power, and abusing the good faith of ordinary folk. But, through it all, your lot made sure that Catholics got nothing. No church, no land, no houses, no jobs, no vote. You didn’t want Catholics to live even.”

Graham responds: “That was ages ago. People don’t think like that any more.”

Joe counters: “Some people do. And your Orange Walks don’t help. Why don’t you just practise your religion quietly like everybody else? The Walks bring all the old stuff to the surface. It’s dead offensive to hear people shouting things against you in public.”

And so it goes on.

However, Breslin believes that what truly divides the city is poverty.

Having spoken to children across the city, both Protestants and Catholics, supporters of Rangers and Celtic, having dug back into her own roots and the experiences of family, friends and acquaintances, Breslin is convinced that neither religion nor football rivalry is the cause of sectarianism.

“When you live in these circumstances, that’s the interest in your life.

It’s something to do, it’s a channel for your energy, it’s identification,” she says.

“It’s all these things that the Nazis used to prey on the youth just before the Second World War when Germany was in a complete decline and had lost its sense of purpose, had a great deal of poverty and a lack of employment.

The kids in these situations are really trapped; they don’t have the wherewithal to get out of it.”

She spoke to boys and girls in Glasgow about their attitudes to supporting Rangers and Celtic and religious divides, describing their anger that “the other side” would not let them display their football colours in public.

She uncovered apparently contradictory attitudes. To her question: “You’re a Celtic supporter. Would you play with someone who’s a Rangers supporter?”, the answer was universally: “Yes.” But ask: “Would you play with someone wearing a Rangers top?”, the answer was “No.”

“I asked if Graham would go to Joe’s house? ‘Yes.’ Would he meet his family? ‘Yes.’ One of them said: ‘How many of them would there be? If there were a lot, that would be frightening.’

“Would you go on the day after a Rangers v Celtic game? ‘It would depend on who won. I would go if we won or if it was a draw.’ But if their club had lost, they couldn’t stand it.

“I thought that was so interesting, what they said about a draw and if there was a really bad foul and someone got sent off. So I wrote about that happening to Graham,” she says.

As a children’s writer, Breslin does a lot of work in schools, many of them in very deprived areas. “You would hardly credit that kids are living in such circumstances. It’s a breeding ground for anger,” she says.

The starting point of Divided City was a request from a teacher that Breslin write a play that could be performed in a classroom in a double period. At the time, the first coachloads of asylum seekers were arriving in Glasgow and community tensions were high.

Her original theme of different languages and communities shifted over time to Scots and their communities, tensions and their differences. Breslin told her publishers that she wanted to write about Glasgow and sectarianism. (The school play has not been written, she confesses.) Divided City is, she believes, the first book for children that relates to the local divisions.

Originally, it opened with Graham reliving in his head the football match he has just played. However, the publishers Doubleday were hesitant about a football theme, so she rewrote the beginning to focus on Graham’s discovery of the injured Kurdish asylum seeker, Kyoul.

“On the one hand, teachers are always saying they are desperate for books about football, but the publishers said that football doesn’t sell,” she says.

That raises a question over whether teachers have identified reluctant readers who might be enticed by football books but that group is not sufficiently large to be worthwhile for publishers.

Even before it is published next week, the novel has been perused by Glasgow’s education advisers. They are unlikely to make it a compulsory text but will almost certainly include it in the books offered in early secondary years in the hope of inspiring reading and debate. It could join books such as Mark Frankland’s The Drums of Hampden and Joan Lingard’s Across the Barricades and The Twelfth Day of July.

Breslin, who has spent much of her working life in Glasgow’s libraries service, hopes that children will read Divided City for enjoyment rather than because it is a prescribed text.

“As a librarian your raison d’etre is to get people reading. By the time boys reach 12 or 13, they can go off reading unless they have developed an interest in a certain thing, like science fiction.”

Divided City by Theresa Breslin, Doubleday, pound;10.99 hardback, published on May 5, for over 10s