By Peter John Meiklem, Media Correspondent

A SAVAGE attack in a new book by a Guardian contributor on the former editor of The Observer is set to ramp up tensions between the sister publications.

In Nick Davies's Flat Earth News, which is published this week, he describes Roger Alton as a sex-obsessed political incompetent who, on being appointed to the editor's chair told David Miliband, then an aide to the prime minister, that he wanted to increase the amount of sport and sex on The Observer's front page.

Davies holds up The Observer in the months leading up to the invasion of Iraq as an exemplar of journalism gone badly wrong. He claims Alton's political inexperience, coupled with the naivety of then executive editor and former Scotland on Sunday journalist Kamal Ahmed, allowed the paper to be manipulated into supporting the invasion.

Davies refused to rule out the possibility the publication of his book led to the resignations of both Alton and Ahmed. They both left in October, shortly after it came to light that the book was to heavily criticise them and had not been actively opposed by Guardian Newspapers editor-in-chief Alan Rusbridger, Alton's line manager.

Davies told the Sunday Herald: "I have no way of knowing if that had any impact on either Alton's or Ahmed's decision - you will have to ask them."

Observer journalists fear the publication of Davies's book will add to tensions already in existence between Britain's two largest liberal papers. A high-profile contributor to The Guardian - and former winner of reporter of the year, feature writer of the year and journalist of the year at the British Press Awards - Davies continued to be paid his retainer by The Guardian while carrying out research on the book. He says, however, that Alan Rusbridger did not know about the book until it was written and later declined to serialise the results.

Davies said: "The idea that the book is Rusbridger's way of getting at The Observer isn't true. In fact, he could see there was going to be a problem and was concerned about that, but didn't interfere because he's not that sort of editor. However, when he found out what was in the chapter on The Observer he declined to serialise the book."

When Ahmed and Alton resigned, they both indicated they wanted to move on to other projects. Before Alton's decision was announced, relations between him and Rusbridger were said to have been tense. Alton is said to have refused to embrace the internet in the way Rusbridger wanted, and was annoyed by the way the two papers were being forced to integrate online. Observers fear Davies's book will be seen in the context of this stand-off.

Davies disagrees: "I've known Rodge for 30 years. We used to play in the same cricket team. I set out with a clean sheet when beginning the research."

Davies said he was only drawn to write about The Observer after an ex-girlfriend, who provided media training to high-profile politicians, suggested he investigate the work of Kamal Ahmed in the run-up to the war.

In the book, he accuses Ahmed of having so close a relationship with then No 10 spin doctor Alastair Campbell that he would run the week's list of news stories past him.

Davies, who claims in his book that The Observer deliberately spiked stories from the paper's US correspondent, Ed Vulliamy, that contradicted Downing Street's line on weapons of mass destruction (WMD), said: "There has been a collapse at the heart of the industry and the WMD stories are a nasty example of that. In the old days, decisions about what stories appeared in the paper were taken in newsrooms; now they are taken by PR experts and people are reading that thinking it is true."

In his book Davies presents research, conducted by Cardiff University's journalism department, that 80% of news stories in the UK quality press are at least partially made up from second hand-material from PRs or from Press Association copy. He claims a smaller number of Fleet Street journalists are now producing three times as many pages as they did 20 years ago. The time pressures this creates, Davies argues, leaves little time for fact checking or contact building and journalists are therefore more liable to make mistakes or to be manipulated.

Asked for his thoughts on the book, Alton responded that he had not even heard of it and knew nothing about the allegations it contained. He said: "The idea that I left The Observer because of this book is about as likely as the Taj Mahal turning out to be a space ship, or the Jews being responsible for 9/11 or that the sun comes up in the middle of the night.

"I left the paper because I'd been there a long time and with the long process of integration coming up I thought it was better to leave the job to someone else."

Kamal Ahmed was unavailable for comment.