Philip Roth once said that when a writer is born into a family, the family is finished. This excellent dictum has been outmoded by publishing practice. Nowadays everyone is a writer, and families are in revolt.

Colin Clark's Younger Brother, Younger Son is not a combative book, yet the very act of writing it is such a wonderful, subtle revenge on the Lord Snooty ethos of his family that the reader is bound to send up a cheer. Mild-mannered Colin is not original like his father Sir Kenneth, or brilliant like his brother Alan - and that's the beauty of it. He is utterly, defiantly cheerful about being neither.

"Brains aren't everything," he pronounces. "I just want to be nice." In the context of the vinegary Clarks of Saltwood, such blandness is dynamite Imagine Alan Clark wanting to be nice. He'd rather hang himself. Imagine Sir Kenneth standing, arms folded, in front of a Leonardo, intoning "Ah yes, what is the lesson of civilisation? Brains aren't everything." And then striding off down a gold-ceilinged corridor, to a surge of grand baroque choral music.

Like most people who believe themselves harmless, Colin's progress through life has left a rather alarming trail of casualties, but he writes nicely; he seems nice; and as an argument for nature against nurture he should be the subject of urgent study. Having already published a well-received account of the Olivier-Monroe film The Prince and the Showgirl (on which he worked as a humble gofer), he now guides us round the foothills of that Himalayan peak - his rather aimless career in TV document- aries, his three marriages, his family, homes, cars; and most important, the famous people he met along the way.

Colin has a tendency to define himself in relation to important, egotistical people. He believes certain individuals (Olivier, Vivien Leigh, Edith Sitwell, Andy Warhol) are naturally "great". Others are "monsters" (though charming). It is a perverse Clark trait to adore those who behave very, very badly, and Colin is fascinated not only by saintly British artists but by grubby con men - one of whom is, fascinatingly, John Le Carre's father Ronnie Cornwell (vividly recognisable from A Perfect Spy.)

Colin is never pushy, but then the door to opportunity stands ajar. He often reminds us that Etonians acquire a useful self-confidence; but he seems blind to the fact that family influence repeatedly saved him from failure. Police charges are always dropped; an Oxford place is unfairly gained; pranks go unpunished. He gets his first TV job when he meets Granada's Sydney Bernstein at a "very grand" party in Venice. (Colin doesn't bother to mention that his father was chairman of the ITA.)

What he shares with his brother is a real gift for anecdote and description. What he thankfully does not share is the "Now look here" tone of voice, or the toe-curling snobbery. He feels obliged to write about art, which is a mistake; he's as uncomfortable in the world of abstract notions as his father was in the world of cuddles. But as for his aim to prove that "it is possible to lead a rich and varied life if you are not great and not that clever... with a little wit and a moderate education" - well, he proves it. Except that, in all honesty, he ought to add "with influence and access to cash", as well.

HarperCollins, pounds 19.99

Lynne Truss