Men dominate the boardroom because most women opt out of the race

At lunch, the female chief executive of a multinational said: "I make sure I have dinner with my daughter every night." So it is possible! Women can have it all! She broke into my reverie. "Then I work until midnight," she added. "Then do some reading so I'm on top of things. Then the car comes at six. I don't need much sleep."

And this is why there are few women at the top. It's a total mugs' game. It is not enough to be good; you must also be a workaholic with the ability to survive on a gnat's sleeping pattern.

Bewail this all you like, but in most of the private sector success demands effort, and rightly so. Margaret Mountford was a partner at Herbert Smith - the type of City law firm that has beds in the basement for wannabe partners who don't have time to go home.

Many women who become mothers decide not to fight to the top of the corporate ladder. They step off - some reluctant, some relieved - and watch their male contemporaries climbing up into the boardroom. Most do not want to emulate Karren Brady, who went back to work three days after giving birth. The money and the kudos are insufficient reward for giving up time at home.

Ms Mountford is entirely right to decry the idea of imposing equality on the top echelons of business. Positive discrimination is utterly demeaning. Neither is it fair that those who toil are bypassed by part-timers, parachuted in to fulfil a quota.

Despite the sexual revolution, most successful men still possess one advantage over successful women: a wife. The modern wife may work, but she does so in a way that allows her to run a home and a family without having a breakdown. The modern wife could be male; it's theoretically a gender neutral role.

The glass ceiling is gossamer thin for women who choose to be the half of the couple who works the necessary hours.

It is women's tendency to select themselves out of the race that leads to male-dominated boardrooms. We must stop getting so uptight about numbers and quotas. Surely we can celebrate our Karren Bradys and Margaret Mountfords without this constant hand-wringing about the women who opt not to follow their example.