You should properly read this after the 9pm watershed, because we are about to discuss a rather delicate matter - Roger Moore's penis.

And it's no good raising your eyebrow in surprise like that, Roger, you mentioned it first, right there in chapter one of your autobiography, My Word Is My Bond (Michael O'Mara £18.99). “Still in my eighth year,” he writes, “I complained to Mum that my ‘wee man' was sore.” The next thing you know, a doctor is bouncing the wee man up and down on the end of a pencil and before long Roger is being wheeled into hospital to be circumcised. Why, hello, Mr Bond, we've been expecting you.

As it turned out, this was the future screen star's first taste of showbusiness. For the next week, members of his gang queued up for a look, and a flasher on Wimbledon Common asked, unsuccessfully, for a private viewing, introducing himself with the words: “Your friend says you have a big dicky.”

I mention all this to highlight a newish fashion in celebrity biography. I've not actually read the memoirs of Noël Coward, but I'm prepared to bet that his foreskin barely got a mention. Yet Moore's revelation is very much the modern way. I would even say he is at the cutting edge, but in the circumstances that would be unkind.

It's the same with Dawn French's breasts in her memoir Dear Fatty (Century £18.99).They're huge, she says (honestly, you could have knocked me down with a feather), and men just don't know what to do with them. Big hands are apparently an advantage because Dawn says that her 42H lady bumps need a lot of stroking and kneading rather than the twiddling, tuning and overzealous sucking that she's had to put up with in the past. Does anybody happen to remember whether the memoirs of Dame Edith Evans mentioned similar problems?

I have just worked my way through six showbiz autobiographies - a drop in the literary ocean of titles published in time for the pre-Christmas frenzy. It was not a job for the squeamish.

Dawn, for example, tells how, while a schoolgirl, she was once groped by a man pretending to be a security guard at the Co-op. She also recalls the time when, as a very young child, she saw her father naked and tried to save him from the pink, snakey creature that appeared to be attacking his groin. The more she tugged at it, the more the strange creature seemed to cling on. “Inexplicably, both of you seemed helpless with laughter and you even seemed to be resisting my help as you pulled on your pants and let the biting thing stay inside,” she writes. “I never saw it again, so I guessed you'd had it put down at the vet's or perhaps left it at the zoo.” Dawn's memoirs are in the form of letters, that one to her late father, who committed suicide when she was 19. They're well written, warm and funny.

Julie Walters has a few tales in That's Another Story: The Autobiography (Weidenfeld £18.99) that will make your toes curl, such as the time she made a plaster cast of her boyfriend's not-so-wee man for a drama-school project. All went well until she tried to remove the cast and he yelped in pain. She eventually freed him, displaying the result on the mantelpiece. By this time, incidentally, she had long got over her problem with bed-wetting. Not to mention the early tightness during sexual intercourse.

You might think all this is too much information, yet it makes a change from the traditional formula of celebrity memoir, which must - under Equity rules - include the following elements:

1 The subject has to have been born into modest circumstances. Full marks on this score to Michael Parkinson who, in Parky: My Autobiography (Hodder £20), opens with the words: “Every morning when I woke, I could see the pit from my bedroom window.”

2 There should be a hint of early promise, such as the nun who told Walters: “You should go on the stage.”

3 He or she decides to be an actor, but must struggle for success. Moore's first wife was convinced he would never make it and the marriage broke up.

4 At last, the big break. The subject then meets Michael Caine, for whom he or she has the utmost admiration and respect, and who later becomes a valued friend.

So, apart from the revelation of widespread genital trauma in the theatrical profession, what are these six books actually like? Moore's is the most traditional. Perhaps the only big surprise is his modesty: he describes his acting ability as “limited”.

For a comedian, Paul O'Grady's life story doesn't have much in the way of laughs. But in At My Mother's Knee: And Other Low Joints (Bantam Press £18.99) you see where he found the inspiration for Lily Savage, the character that made his name. She was the soundtrack to his childhood - the voice of strong women bellowing to each other in industrial-strength Scouse. He talks about his brief career as a housebreaker, but if you want to learn about his life as an entertainer you'll have to wait for the sequel. As this book ends, he has just chucked in his job washing dishes at a Sue Ryder home, his father has had a fatal heart attack and his girlfriend - no, really - has just announced that she is pregnant.

Parkinson's memoirs resemble a long and affable lunch in his company as he traces his career from national service as the youngest captain in the British Army, through local newspapers to television reporting and chat-show stardom. He tells a good story. One weekend he had George Best to stay. On Monday, his son, also called Michael, was asked what he had done at the weekend. “I played football with George Best,” he said, and was made to stand in the corner for telling tall tales.

Walters's book - also well written - has moments of Alan Bennett warmth: such as the time when her mother, after learning French at evening classes, offers Julie a coup d'état, believing it was French for a cup of tea.

Richard Madeley's Fathers & Sons (Simon & Schuster £18.99) isn't really an autobiography. At its centre is the story of his grandfather, Geoffrey, whose family emigrated to Canada when he was only 10, leaving him to work on his uncle's farm in Shropshire. When Geoffrey eventually inherited the land, his uncle's will forced him to share it with his brothers and sisters. The effect of that betrayal echoed down the generations: Madeley's own angry father beat young Richard with a cane until Richard's mother threatened to call the police. As I said, this isn't autobiography at all - it's therapy. And after reading Geoffrey Madeley's story, a few theatrical anecdotes - even ones that involve James Bond's wee man - seem rather tame.

Times Recommends

• If you only buy one book this Christmas make sure it's...
• The Times Christmas Books 2008: Gifts
• 10 Books Not To Read Before You Die