A book on murder cases found in his grandparents' house at the age of 14 had a lasting impact on Ludovic Kennedy. He looks back on a life campaigning against miscarriages of justice, including the cases of theGuildford Four and the Birmingham Six

Ludovic Kennedy's CV could be shared out among half a dozen people and still look impressive. But what Scottish-born Kennedy, now 82, is most famous for is his lifelong campaign on behalf of people wrongly convicted under the British legal system.

He has worked as a current affairs broadcaster and as a documentary-maker, and his 20-plus books include titles on history, religion, travel and his own life, in addition to several on crime and the legal system. He fishes, plays golf, collects fine art, reads poetry, and can turn a nifty heel in a Highland reel. His dancing ability may have something to do with being married to the acclaimed former ballerina, Moira Shearer, who achieved worldwide fame in the classic 1948 ballet film, The Red Shoes.

When Kennedy was a boy in Edinburgh, he spent a considerable amount of time at his grandparents' house. His grandfather, after whom he was named, had been professor of public and international law at Edinburgh University, and possessed a large library of books about legal matters. While staying there at the age of 14, Kennedy found on an upper shelf several volumes of a series called Notable British Trials. Within their covers were studies of fictional-sounding but true crimes and trials, including those of a 20-year-old woman who poisoned her lover with arsenic, and of a doctor who murdered both the family maid, with whom he had been having an affair, and his wife, disposing of the bodies by chopping them into small pieces and dropping them down a gorge in Dumfries. This was in an era when murderers were still hanged.

The editor of the series, William Roughead, was a friend of his grandfather's and sometimes came for tea - which, for Kennedy, was like "meeting God".

"Murders and adultery - to a 14-year old awesome and thrilling subjects illustrative both of the weakness and the wickedness of grown-ups," writes Kennedy in the prologue to his new book, Thirty-Six Murders and Two Immoral Earnings.

However, the cases recorded in Notable British Trials made a more lasting impact on Kennedy than the ephemeral thrills. He began to meditate on the finality of legal decisions that deemed a person guilty of murder at a time when death was still the penalty. The result of this musing was that most of his adult life was spent in campaigns against possible miscarriages of justice.

Thirty-Six Murders and Two Immoral Earnings could be described as a - horribly, compulsively readable - condensed version of the major cases which Kennedy, as broadcaster and writer, has concerned himself with over several decades. Speaking by phone from his Wiltshire home in England, Kennedy makes it clear that his (mainly proven) mistrust of the British system of justice over the years has not changed.

"The system of justice here is one which leads to corruption," he states flatly. "Other countries don't have the same history of miscarriages of justice that Britain has. Our system of justice is a recipe for miscarriage of justice and I'd like to see it changed to something more like the European inquisitorial system."

Among the cases covered in the book are those of the Birmingham Six, the Guildford Four, and Iain Hay Gordon, who was wrongly imprisoned for 48 years for the murder of Patricia Curran in Whiteabbey, Northern Ireland. This case was the subject of Eoin MacNamee's recent book, The Blue Tango, which Kennedy is intrigued to hear about, asking me for the publisher's name and saying he wished he'd read it before editing the Gordon chapter of his own book.

Also covered are such cases as that of Timothy Evans, wrongly convicted of killing his wife and baby in 1959 and subsequently hanged. A fellow resident of the shared house, the notorious John Christie, was later found guilty of the double murder (and others).

Given that, as in the Evans case, it is impossible to reverse the execution of an innocent man, why does Kennedy think the US retains the death penalty in some of the less enlightened states? "I don't think they worry too much about miscarriages of justice," is the dry answer. "America likes to think it's a frontier society. Executions are part of that macho image. They're a forward-looking people. They cut no machinery for looking back." He cites this American dislike of retrospection as a main part of his failure to overturn the findings in the case of Richard Hauptmann, who was found guilty of kidnapping and murdering Charles Lindbergh's small son in 1932. He was electrocuted in 1936 for a crime which he maintained until the end that he never committed.

In 1981, Kennedy saw Anna Hauptmann on US television, still protesting her husband's innocence. He was convinced enough to focus his efforts on the case for four years, which resulted in a book, The Airman and the Carpenter, and a film. But there was no subsequent national desire or stomach for a re-examination of one of the US's most notorious cases, and the original verdict stands to this day. This is the only case in which Kennedy admits "total defeat".

IT IS striking that almost all of the protagonists in this book are men, whether they be suspects or representatives of the law. It is in a predominantly male environment that "confession evidence", of which much is written in the book, is extracted. Kennedy describes the technique of depriving suspects of food and sleep for extended periods, and repeatedly questioning them until they break down and sign prepared confessions. This was the method used in the cases of the Guildford Four and of Iain Hay Gordon, among others.

"Confession evidence was the worst, most corrupt thing within the system," Kennedy states. "No jury can ever believe that someone would confess unless they were guilty."

Does Kennedy think women police officers might have approached questioning in a different manner, given much of the "confession evidence" also involved physical brutality? He thinks about this for a while and agrees it is a possibility, although, like anyone concerned with the law, you get the feeling he's far more interested in hard facts than in speculation. The book, incidentally, is dedicated to Gareth Peirce, who acted for both the Guildford Four and the Birmingham Six and whom he cites as the "doyen of British criminal defence lawyers".

For years, Kennedy was sent cases on a weekly basis by the family members of many accused, in the hope that he would take them up. He could, of course, follow up only a handful.

"I have never embarked on a case where I was not absolutely certain it was right to do so," he says. "It's a gut instinct in the initial stage and then I consult the accused's solicitors and if they are convinced of innocence too, I will go ahead."

He has - mostly - been justified in his choices. However, one case he championed for a long time was that of James Hanratty, hanged in 1962 for a murder he said at the gallows he did not commit. In March 2001, a DNA sample extracted from Hanratty's exhumed body was matched by forensic experts to two samples from the crime scene, and his guilt was conclusively proved. That case, of which Kennedy has written in the past, does not appear in this collection, which is a pity, since being foxed from the grave can surely be just as interesting, occasionally, as being a champion of the innocent in their graves.

Thirty-Six Murders and Two Immoral Earnings by Ludovic Kennedy is published by Profile Books at £16.99 sterling