THE critics' knives have been waspishly filleting Robert Lacey's book on Sotheby's, admiring its style while declaiming its content. Their worries centre on what is not there rather than what is: no mention of the British Rail Pension Fund's expensive foray into fine art; barely more than a sniff or two at some of the shenanigans that take place behind the green baize doors; far too much time spent on the trivia sales - the frills and furbelows of the Windsors and Jackie O.

Lacey acknowledges some of this, admits to his own partial seduction by that lethal perfume of wealth and class: ''I love all the razzmatazz, the snobbery of Sotheby's. I love the vicarious contact with money. But at the same time that I was being so superior about people paying #20,000 for a piece of the Windsors' wedding cake, I got involved in some bidding myself.''

The evidence is his acquisition of the Duchess of Windsor's weighing scales, kept in his daughter's bedroom and wheeled out for the entertainment of curious strangers. Lacey paid $1000 for them: ''It was late at night and I heard the bidding stop at around $700. And there were the scales, white enamel, like the ones you had at school medicals, straight out of The English Patient.''

And, in that moment, he turned into the classic Sotheby's punter. A man who had managed to live without tall, white enamel weighing scales became a man who just had to have them, discovered he had always wanted some. Of course, he says he wouldn't have gone over that thousand (''Well perhaps 11 or 12 hundred.'') but his history book of Sotheby's is full of the tales of people who went on bidding, some of whom overreached themselves, others who bid so much they ended up buying Sotheby's itself. The auction house is now ''the Property of an American Gentleman'', one Alfred Taubman, and the director is another American, ''Dede'' Brooks. Everything is for sale to the highest bidder.

Lacey's own history is one touched tangentially by both money and class; he is, he says, ''aspirational''. A Bristol Grammar School boy, son of a bank manager, he won a scholarship to Cambridge where he read History. His greatest ambition was to be a don but his tutor told him he wasn't bright enough: ''He thought I could go to a provincial university and be a lecturer there, but he said that he couldn't help feeling that I loved the ivy-clad walls, the dreaming spires, and he was right.''

There was another option, more attractive than that of home-spun provincial academia. Lacey was put in touch with M15 who asked him if he'd like to ''be of service to Her Majesty overseas, in a 'confidential capacity'.'' Lacey read this, no doubt correctly, to mean spying.

There then followed a year of interviews and tests culminating in a final meeting with a psychologist: ''She told me that I would not be a James Bond, I would not have a licence to kill, the work would be very bureaucratic, dogged by office politics, and that, by the age of 30 or so, even though I might have earned a lot, it would have to be a light hidden under a bushel. In the eyes of the world, I would appear to be a failure. This was the first time that I gave it serious thought. I decided I wouldn't do it.''

Instead he entered a story-writing competition, won fourth prize, and, as a result, successfully pieced together a life as a journalist and, latterly, a writer. His books have wealth and class in common: Majesty - a biography of Grace Kelly, wife of Prince Rainier of Monaco; and Aristocrats. But Lacey won't easily allow the view of his work as the scribblings of a simple snob, describing himself instead as a ''sympathetic outsider'', observing the snobbery, and the passions, of others.

His interest was excited by the early and present history of the London auction houses as well as by the relationship between money and art, the ''bidding for class'', the possession of others' creativity.

''I can't get that indignant about the wicked things that go on, it seems to me to be the way of the world. All the reverence that is attached to art can also be transferred to the auction process and elevated from being a seedy sort of redistribution into something dignified. But it still remains commerce at the end of the day; there is a conflict between the two.''

And we stand for a while, pondering this thought and revering the glorious art and commerce that is a pair of used weighing scales.

n Sotheby's: Bidding for Class by Robert Lacey, published by Little Brown at #20. Robert Lacey will be visiting the Royal Concert Hall on May 28 at 1.00pm.