By day, she is a 63-year-old social worker in Birmingham, specialising in adoption and fostering. By night, she works away in her made-up world. Yesterday, Gaynor Arnold was astonished to discover that her first novel had been nominated for one of the world's leading fiction awards.

Having devoted almost 40 years to caring for others, she found herself hurled into the limelight, as one of 13 authors singled out for this year's £50,000 Man Booker Prize.

She is up against two former Booker winners, Salman Rushdie and John Berger, and four other debut novelists.

Under the chairmanship of Michael Portillo, the former Cabinet Minister, the judges were impressed by Arnold's Girl in a Blue Dress, her fictionalised account of Charles Dickens's troubled marriage.

"Here is somebody who can tell a story," the judges told one another during a meeting that lasted just 40 minutes, so agreed were they on their choice.

For Arnold it was all the more rewarding because publishers rejected an earlier manuscript. A literary agent turned down this one as well.

Refusing to give up, she submitted it to a small publisher in her home city, Tindal Street Press, which saw its potential immediately.

Founded a decade ago, the company has only two full-time members of staff and brings out just six books a year. Yet its track record in spotting talent is considerable. Arnold is its third author to have been shortlisted for the Booker, not to mention other awards, in the last six years.

Speaking to The Times shortly after hearing the news, Ms Arnold said: "It's nice to know that all the hard work has been validated."

As she works "almost full-time", writing in her spare time was difficult as social work "can be quite stressful," she said. Girl in a Blue Dress took her five years.

The daughter of shop assistants, who describes her family as working-class but who studied English literature at Oxford, said that holiday photographs always show her "nose in book".

The longlist was chosen from 112 entries. The youngest selected author is 29-year-old Londoner, Tom Rob Smith, whose first novel, Child 44, set in Stalin's Russia, was published after a bidding war. The oldest is 81-year-old John Berger, a writer and art expert who was picked for From A to X, a series of letters between a woman and her lover.

They face competition from Rushdie, the Anglo-Indian author whose Midnight’s Children won the Booker almost 30 years ago and was voted by the public the greatest Booker prizewinner of all time earlier this month. This time, he is up for The Enchantress of Florence, a 16th-century story which the bookies immediately installed as their overall favourite.

Its admirers included John Sutherland, the academic who proclaimed that if it “doesn’t win this year’s Man Booker I’ll curry my proof copy and eat it".

The Booker is celebrating its 40th anniversary this year. Any full-length original English novel, written by a citizen of the Commonwealth or the Republic of Ireland published this year, is eligible for the prize.

The 2008 list reflects a wide geographical spread, with The White Tiger by Aravind Adiga, who lives in Mumbai, A Fraction of the Whole by Steve Toltz, from Australia, and A Case of Exploding Mangoes by Mohammed Hanif, who was born in Pakistan and lives in London. All are first novels.

This year's judging panel featured Alex Clark, literary journalist; Louise Doughty, novelist; James Heneage, founder of Ottakar's bookshops, and Hardeep Singh Kohli, TV and radio broadcaster.

Mr Portillo claimed to have read 105 of the 112 entries from start to finish since January: "There were a few where other (judges) said they were 'a complete turkey' and I didn't trouble myself with those."

Although he applauded the overall quality, he revealed that one of the other judges "thought they were average".

Notable omissions from the list included Peter Carey, who has won the Booker twice before and was widely expected to be back for Illegal Self, an acclaimed psychologically-taut novel.

The 13 names will be whittled down to six on September 9 and the overall winner will be announced on October 14.

Winning is a sure guarantee of a huge sales increase. Anne Enright's The Gathering took the 2007 prize and went on to sell 646,000 copies in the UK, Ireland and America. Until then, she had sold just a few thousand.

The longlist

Aravind Adiga The White Tiger
Gaynor Arnold Girl in a Blue Dress
Sebastian Barry The Secret Scripture
John Berger From A to X
Michellede Kretser The Lost Dog
Amitav Ghosh Sea of Poppies
Linda Grant The Clothes on Their Backs
Mohammed Hanif A Case of Exploding Mangoes
Philip Hensher The Northern Clemency
Joseph O’Neill Netherland
Sir Salman Rushdie The Enchantress of Florence
Tom Rob Smith Child 44
Steve Toltz A Fraction of the Whole

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