Isabel Oakeshott is writing a biography of David Cameron with Lord Ashcroft and was Political Editor of the Sunday Times

Spare a thought for Jeremy Hunt, who this month finds himself without either of his special advisers.

Last year, the Health Secretary appointed the impressive Christina Robinson to cover for his long serving media SpAd Sue Beeby while she was on maternity leave.

Now Robinson herself is off with a newborn, and Beeby has yet to return. Hunt has had to draft in yet more cover.

It says a lot about Hunt – who has two young children himself and a third on the way – that he was willing to get himself into this predicament. To his own detriment (because the relationship between a Secretary of State and SpAd is very personal and one of great trust) and to the potential detriment of his media coverage, he nevertheless hired a second woman of childbearing age to stand in for the one he had temporarily lost.

All credit to him. Many employers recruiting for core positions would simply avoid this risk. Since they are quite rightly prevented by law from asking female candidates about their private lives, they must either gamble that a woman of childbearing age has no immediate plans to start a family – or hire a man with equivalent, or even weaker, credentials and avoid the risk.

Statistics published by the Ministry of Justice this month revealed a sharp fall in the number of sex discrimination tribunals. Yet official figures never tell the real story. The truth is that many employers, particularly those running small firms or recruiting to sensitive posts, make a rapid mental calculation when a woman of childbearing age presents herself for interview.

Unable to ask a straight question of the potential candidate, bosses will go with whatever flimsy clues are available, to figure out the odds of a woman taking maternity leave any time soon.

A well known PR company chief once told me straight up that he would never hire me, because I was recently married and bound to have children. I was dismayed, but in a way I admired his honesty.

This is what ambitious young women are up against. Getting hired is just the first hurdle: retaining and building a career which is interrupted by one or more periods of maternity leave is an extraordinary challenge on so many levels. That’s just how it is.

As for getting promoted while pregnant, save in the most progressive workplaces, you can pretty much forget it. I once hid a pregnancy for months while a boss dithered over whether to give me a big job. There was no hard evidence that I would be discriminated against but I knew my growing bump would not help.

By the time I reached 26 weeks, he still hadn’t made up his mind and I was forced by law to reveal my condition. In the preceding weeks I had near enough taken to walking backwards out of the office so he would not see me sideways.

He ended up promoting me anyway. Perhaps the risk of discrimination had been all in my mind, but we all know babies are no asset to women trying to climb the ladder.

Sadly there’s no easy answer. Women applying for new jobs or promotions who plan to have children in the short or even medium term would be mad to show their hand.

But women who do not want children in the near future or have already completed their families should do themselves and employers a favour by removing the guess work. They should simply volunteer the information.

That way bosses will know they’re not likely to suffer a Jeremy Hunt – and they can succeed or fail on their merits.