In the foreword to David Niven: The Man Behind the Balloon, Michael Munn confesses that he can't be an objective author with this biography because he is part of it.

Michael Munn

JR Books, €23.70

"I couldn't write it any other way," he states. "It may not seem apparent from the outset, but David Niven would approve. It was, after all, his request that I write it."

But for all the author's obvious respect and affection for his subject matter, this is no Hollywood hype or fawning hagiography.

Munn reveals that, despite his dazzling on-screen persona, Niven wasn't always the perfect gentleman. He was insecure and sometimes used people to get ahead. And his philandering was legendary.

But he did "at least try to be a decent man".

This is particularly evident in the book's opening chapter where, ravaged by motor neurone disease, the dying actor attempts to set the record straight in a series of extraordinarily frank and revealing interviews.

These, together with a series of interviews with Niven's second wife Hjordis and many of the Hollywood stars who worked with him, form the basis of this forensically researched and wonderfully candid biography of a man who was infinitely darker and more complex than his bright and breezy on-screen persona would suggest.

Even Niven's parentage wasn't what it seemed. Though registered as the son of his mother's husband, he was in fact the result of one of the many extra-marital flings she enjoyed while her husband was off fighting for king and country in the First World War. Following Niven senior's death at Turkey's infamous Suvla Bay, Niven's mother went on to marry his biological father, the Conservative politician Sir Thomas Comyn-Platt, but it was years before the true father/son relationship was acknowledged.

In the meantime, young Niven was packed off to a private prep school where he was mercilessly bullied, beaten and sexually assaulted: "I felt that I would never forgive my mother and stepfather for sending me there."

After a spell in hospital occasioned by the effects of bad food, Niven's mother moved him to an expensive private school in Ascot; here, happy at last, his talent for entertainment and prank-playing came to the fore.

"By then I'd discovered that by making the other boys laugh I became popular, and I admit I wanted to be liked. Well, don't we all?"

Expelled for a particularly audacious prank (he posted a matchbox full of dog's mess to a friend in a nearby school which was opened by Matron) Niven was packed off to a series of schools before finally ending up in Stowe, where the headmaster, John Fergusson Roxburgh, became "the next best thing to a father" to him.

"He changed me for the better," Niven recalls. "I had been turning into an evil little bastard, but going to Stowe School turned my life around."

Its end-of-term concerts also gave him his first taste of the stage. He instantly took to it, not because he wanted to be an actor, but because "I simply wanted to be liked".

Niven went on to hone his acting skills at Sandhurst military college, after which he blazed a trail to Hollywood via high-society friends and well-practised seduction skills. He was privately coached by Merle Oberon, Britain's biggest movie star, with whom he'd had an affair in London. They lived together for a while in Hollywood but Niven found it impossible to be faithful to her, or to anyone else.

Following their break-up, he copper-fastened his reputation as a ladies man by moving with fellow hell-raiser and philanderer Errol Flynn to a house aptly called Cirrhosis-by-the-Sea. However, when it became apparent that Flynn's sexual preferences were dictated by whatever was immediately available, Niven quickly flew the love nest.

The outbreak of the Second World War brought him back to London where he met airforce cipher clerk Primula (Primmie) Rollo.

It was, he says, love at first sight and they married in a little church on Wiltshire Downs as the Battle of Britain raged above.

"When we were together," Niven later wistfully recalled, "I enjoyed every minute, every second. I was never happier in my life than when I was with her. Never."

The couple quickly went on to have two sons, but tragedy struck at a party at the home of movie star Tyrone Power. Whilst playing a game of hide-and-seek, Primmie mistakenly opened a cellar door and fell 20ft to her death. She was just 28. Afterwards, crazed with grief, Niven put a gun to his head, but the trigger jammed; he took this as a sign from God that he should carry on living for the sake of his children.

A disastrous second marriage followed. Swedish model Hjordis Paulina Genberg was a heavy drinker beset with mental illness, who seemed hell bent on making her husband's life as miserable as possible.

Despite this, Niven never blamed her for their sham of a marriage, not least, says Munn, because he knew that the problems they had were as much his fault as hers, and he stuck with her till the end.

As his career flourished, and his suave and polished on-screen persona became almost an extension of his own, Niven became a hit on the chat-show circuit, telling tall, self-deprecating tales that had audiences in stitches. These stories eventually formed the basis of his much acclaimed memoirs The Moon's a Balloon and Bring On The Empty Horses. These, Munn asserts, even more than his films, are Niven's greatest legacy.

At his funeral, among the flowers that adorned the church, was a huge wreath from the porters at Heathrow Airport with a card that read: "To the finest gentleman who ever walked through these halls. He made a porter feel like a king."

This, says Munn, pretty much summed up David Niven.

"He was a fine gentleman and a very English one at that, which is no bad thing in this day and age. He wasn't perfect, of course, but he was a decent man to those who came into contact with him -- it didn't matter what class you were. You could be a hotel porter, a member of royalty or just a mere messenger boy as I was when I first met him back in 1970."