Walsh's own apology - his afterword - states: 'Everybody knows Casablanca. Everybody loves Casablanca. Therein lies both the challenge and the danger' - has done nothing to stop the tomatoes flying.

The title is pulled from the signature tune punched out by Dooley Wilson - who played Sam, the pianist - and sets the tone for a novel that filches and reinterprets many of the best lines of arguably the most quoted movie in Hollywood history.

Many critics grumble at his use of the great quotes - but are not above hijacking these themselves in their criticism.

'I suppose you know this is not going to be very pleasurable for either of us,' one reviewer writes on the Amazon site. 'So said Louis Renault in the film . . . and unfortunately it applies to this book also.' Many have received the book with mixed-feelings, but for the die-hard fans, it is merely too contrived and cliched. Others express personal hurt, writing of 'blasphemy' and 'a hanging offence', but still, like book-burners everywhere, betray the fact that they have, nevertheless, brought and devoured the work.

As Time Goes By starts where the film ended, with Ilsa (Bergman) and her Czech resistance-hero husband Victor Laszlo leaving for freedom on the plane to Lisbon. The world-weary bar-owner Rick Blaine (Bogart) and French police captain Renault slope off into the mist and uncertainty to start the 'beautiful friendship' as the evil Nazi, Major Strasser, lies bleeding on the runway.

The book entails all the original characters in some form, most of whom find themselves in London and wrapped up in a British attempt to kill the notorious Nazi boss Reinhard Heydrich in Prague.

This part of the plot is 'messy and confused . . . episodes of [television series] Hogan's Heroes had more credibility', one reviewer charges. 'The movie had plot holes the Germans could have driven armoured divisions through, but got away with it because of its stylishness and emotional intensity. But Walsh's often purple prose can't distract from his plot problems.' Where Walsh seems to have more success - and probably pulls in the punters - is in filling in the backgrounds of the characters who meet for three nights and two days in the slice-of-life original. His work is as much prequel as it is sequel. It is also where, by Walsh's own admission, he takes his biggest risks as the ambiguity in Rick's past has grown into a key device in the film's on-going popularity.

Ilsa is the daughter of a heroic Norwegian politician - meaning Laszlo is something of a father figure, readers learn, but the real controversy starts with Rick, who many fans like to think of as the fallen son of a rich family. Richard Blaine started life as Yitzik Baline, a Jewish gangster and speakeasy owner from East Harlem who fled the country after a messy killing and a love affair with a gang boss' daughter.

Walsh goes into considerable depth in his afterword to explain himself, acknowledging the prospect of heated controversy, while weaving a literal theory through the loose ends in the original plot.

It does get absurd. At one point one character notes the ease with which Rick turfs a German out of his bar: 'It looks like he's been doing it all his life.' Rick replies: 'What makes you think I haven't?' With regards his ethnicity, Walsh notes all the key creative forces behind the original script were Jewish. It was also the custom in Hollywood at the time to disguise Jewish characters as 'WASPs', he says.

'He is a political leftist. His best friend is a black man. He is handy with a gun. He runs a saloon,' he adds.

Unavoidably, the work is steeped in modernity that shows through in its political correctness, some critics allege. Walsh even apologises for the constant drinking and smoking descriptions that pepper the book as in the film.

As the debates rage, Walsh can be sure of one thing as he reflects on his own hill of beans. When - and if - a film based on his book ever comes out, perhaps he should leave town for a while.