The Bloodhound v the Blacks

Lord Black is not pulling his punches. The embattled former owner of the Telegraph Group, who next month faces trial in Chicago on racketeering charges, has issued a [pound]5m libel claim against Tom Bower, the British investigative author and journalist. According to Lord Black, Bower's book, Conrad and Lady Black: Dancing on the Edge, is "vindictive, high-handed, contemptuous, sadistic, pathologically mendacious and malicious".

Bower is not worried. Last week he emailed The Globe and Mail, the Toronto-based Canadian national newspaper, to explain: "Robert Maxwell sued me many times and look what happened to him."

The late owner of the Mirror Group was not his only enemy. Mohamed Al-Fayed is reputed to splutter obscenities at the mere mention of his name. Stephen Byers, the former Trade Secretary, once instructed his lawyers to end distribution of The Paymaster, Bower's biography of Geoffrey Robinson. Chancellor Gordon Brown, whom Bower has depicted as an "inverted ideologue," is said to resent him.

Small wonder. Bower is the most effective journalistic sleuth of his generation. His formidable, legally trained intellect has detected wrongdoing and exposed hypocrisy from the shattered ruins of post-war Europe to the boardrooms of English Premier League football. He gave up being a barrister to join the BBC in the 1970s, where he worked on Panorama and made an early documentary about Maxwell's empire. He has been smashing icons and tarnishing reputations ever since. In his biography of Brown, he wrote: "I have always been invigorated by the calculated snubs of the rich and powerful." His output of critical, revelatory and commercially successful books proves it.

Bower's early work included The Paperclip Conspiracy (1987), an impressively documented exposure of the frantic rush at the close of the Second World War by America, Britain and Russia to locate the German scientists who developed the V-2 rocket and employ them in their own arms industries. He was outraged to discover that Nazi scientists who supplied advanced technology were routinely forgiven for war crimes.

The same tone of principle betrayed is vivid in his other bestselling works of historical detection, including his biography of the Gestapo chief and torturer Klaus Barbie and Blood Money: The Swiss, the Nazis and the Looted Billions, in which Bower presented the first fully documented account of the 50-year conspiracy that allowed Swiss bankers to profit from the atrocities of the Holocaust. Colleagues from his early days at the BBC say Bower's experience in TV made him acutely aware of the value of human angles in investigative journalism. "His historical work is serious, academic stuff, properly sourced and researched," says one. "But right from the beginning Tom was telling the victim's story and including colour." He maintained that approach in highly critical, unauthorised biographies of Maxwell, Al-Fayed, Brown and Sir Richard Branson.

But critics say his human sympathy is reserved exclusively for the victims of those he depicts as too powerful, ruthless and ambitious. "He takes a very pessimistic view of human nature," says a fellow journalist who sat beside Bower at a dinner at the British Museum last month. "He is healthy and superficially avuncular, but there is an unmistakable impression of, 'if you have got something really nasty to reveal about anyone, do, please, come and sit next to me." Peter Preston, the former Guardian editor wrote recently: "The premier bloodhound of British journalism [presents] a formidable array of facts and fiddles. Yet you need a little human understanding in the mix as well. And that ... is not Bower's forte."

High-profile legal disputes are, however. His investigations of the rich and powerful have provoked numerous writs as those people fight to keep secrets he prides himself on exposing. Very occasionally he loses. Maxwell won 10,000 francs from him in a French court using French secrecy laws, prompting Bower to tell the BBC of his hostility to the introduction of similar laws on this side of the channel. "I think that a privacy law would only protect the guilty and the people whose exploits should be discussed," he said.

He does not extend such openness to the details of his own life. My calls to his home telephone reached an answering machine that directed me to dial his mobile. This in turn converted my call into a text message giving my number. Bower did not respond. One former publisher has explained that he routinely declines interview requests and invitations to comment, because "otherwise the people he writes about might find a way of getting back at him".

Bower works from home, a large house on Hampstead Heath that he shares with his wife Veronica Wadley, editor of the London Evening Standard, and their two children. He can occasionally be seen walking in the area and one near neighbour describes him as "very sleek, contented and healthy looking". He is a member of the Garrick Club and a regular contributor to Private Eye, which repays the honour by paying meticulous attention to his legal adventures.