Until November 1989, the Berlin Wall stood as a stark icon, splitting a city and defining a political era. Now, from the rubble of the division between east and west Europe, a book on the subject is establishing itself as a landmark of contemporary culture.

Stasiland, Anna Funder's award-winning exposé of the devastating effects of the work of the secret police inside East Germany, is leaving bookshops at a rate rarely seen with serious factual works. Reaction to the book, a series of extraordinary personal stories told to the first-time author, recalls the excitement around Antony Beevor's Stalingrad, another unexpected historical hit. Funder, like Beevor with his book in 1999, has caught the public imagination and crossed over into the popular market.

There is already film interest in Stasiland, with approaches to Funder's agent from both British and American film-makers who hope to develop a script using two or three of the most poignant and bizarre stories. This month, again following in the footsteps of Stalingrad, Stasiland won the respected £30,000 Samuel Johnson Prize, ahead of titles by established authors such as Bill Bryson's A Short History of Nearly Everything.

'The prize has made an enormous difference, of course,' said Sarah Holloway, Funder's editor at Granta. 'We now have 42,000 copies in print, double what we had before, and we will probably reprint before long.'

The widespread appeal of Stasiland is founded in part on the vogue for kitsch Eastern bloc memorabilia, or 'Ostalgie'. Last year's acclaimed comic German film Goodbye Lenin showed how exotic the sad lives of families split by the Wall appear when observed from a distance of a decade and a half. Stasiland and Granta, its publisher, have capitalised too on the renewed general appetite for history books, reflected in the sales of David Starkey's book on Henry VIII's wives last year and on Simon Schama's A History Of Britain in 2000.

'There is an interest now, 15 years after the Wall fell, in learning what societies were like when the world was divided into two,' said Holloway. 'It is a country that has ceased to exist, and what is more it is an extremely well-written, moving book.'

But the real reason why Funder's book, first published in Australia, will soon be found on many bookshelves all over Britain is the pace of the shadowy story she tells. At times it reads more like a thriller than a historical survey. Funder, an Australian German-speaker who had worked for the federal government before taking up writing full-time, advertised in the personal column of a Potsdam newspaper asking for former Stasi men to contact her 'with a view to conversation, discretion guaranteed'. Many responded - which Funder, 37, puts down to her nationality. They felt free to talk to an outsider.

'I loved her voice in the writing,' said Holloway. 'It is not like other history books where the author pretends to be objective and uninvolved. It isn't a quick journalistic book either, she didn't just go over and do a snapshot. She had actually lived there.'

Some passages of the book are reminiscent of Graham Greene's portrayal of the search for Harry Lime in The Third Man, or perhaps of scenes from Len Deighton novels in which his laconic spy, Harry Palmer, is confronted in dark alleys by communist agents in cheap macs. Funder tracked down a former Stasi lieutenant-colonel who worked in Division X, one of the most secret divisions of the overseas spy service. He tells her that after he had identified himself publicly he lived in fear of Stasi reprisals. 'I mean I used to check my car to see if it had been tampered with, but there's not much point doing that because if they're any good they do it so as you can't tell,' he tells her in a dark bar.

Although Funder's book chronicles an extinct society in which an estimated one in every 63 citizens was an informer and in which secret police files outnumbered the documentation for the whole of the rest of German national history, it is also funny.

There is black humour in the absurd practices of the Stasi, which used to irradiate people so that they could be traced later. It also stole underwear from their chest of drawers in case it was needed to give dogs a scent to follow in a chase.

'It is this side of Stasiland that makes it different from other books about the Soviet bloc,' said Holloway.

· 'Stasiland: Stories From Behind the Berlin Wall', Granta, £7.99.