Back in the 70s, when I was looking for my first job in the law, it was hard to be taken seriously as a woman lawyer. It was commonplace for women candidates to be told, "we don't take women" or "we've already got a woman", comments that would be unthinkable - and unlawful - today. Looking back I am amazed that I actually managed to get a foot on the first rung of the career ladder, let alone climb higher.

When I was finally accepted into a set of barristers' chambers as a pupil - a kind of apprentice - there were so few practicing women barristers that it was difficult to find any female role models. And at the time, the perception of women in the law was that we didn't really count because we would eventually leave when we had children and not return.

But being a woman wasn't my only obstacle. Many of my new colleagues were from wealthy families and had been to private schools and I was very conscious of my ordinary background. I knew nothing about the unwritten rules of behaviour in the profession and was constantly putting my foot in it. All in all, I felt out of place and lacking in confidence.

But I was fortunate to get some support early on from Derry Irvine, a senior barrister who agreed to accept me as an apprentice. He was an extremely good teacher and became my mentor. He took the time to show me the ropes, gave me one-to-one tuition and set an example for me to follow, like the technique of how to argue a case - (you must tell a story!) - that I still use to this day.

Huge progress has been made since I first started out as a barrister. These days pupils are chosen by committees, and the numbers of women and men in the law are today about the same. Similarly, in the majority of professions and in work places up and down the country, there have been significant advances. Women not only find it easier to get a foot in the door. They routinely reach positions of responsibility and status. But once you get near the top of a company, you find all too often that women are as rare as they were throughout the legal profession in the 1970s.

The reason for this is obvious. Most women lead a double life. They are the main person responsible for child-rearing and they are also trying to hold down a job. They are the ones who dash home guiltily after work to get their children's tea, while their male colleagues work late to show their commitment, or network after office hours in the pub and on the golf course. What woman has time to fight her way further up the career ladder?

Part of the answer of course is for fathers to share the child rearing, so that mothers have more time to level the playing field at work. There are it's true an increasing number of fathers who now give up their job to look after their children, allowing mothers to develop their careers instead. But that doesn't constitute 'sharing' childcare - it merely changes the roles of men and women around. Real sharing of childcare will require an enormous cultural shift.

But rather than sit back and wait for change to happen, women can make a difference by making changes themselves. We can help each other up the ladder. We see men - despite their often more competitive natures - mentoring one another, encouraging younger men to succeed and actively promoting them, in the way that Derry helped and encouraged me early on in my career and others did later on too.

Women often complain about lack of opportunities and about not being promoted - and there's justice in many of those complaints - but we all need to help those lower down the ladder too. We need to take a leaf from the men's book and do more to encourage and support women trying to further their careers. If we want more talented women rising through the ranks, if we want to create a pipeline of talent to executive and board level positions, that's got to be part of the solution.

It may be the right thing to do, but make no mistake, it can help your own career too. Men know this. They know it makes business sense, because nurturing talent is an important part of being a leader and mentoring someone provides an opportunity to develop that skill. When you engage in a mentoring relationship, you're forced to see things from another's point of view. Whether it is because you're working with someone from another culture, dealing with another type of business or working with a different age group, mentoring gets you thinking in new and different ways. Mentoring can also be the spark that leads to renewed commitment to your own business or career.

The internet is a godsend to mentoring, making it possible to mentor wherever you are. A branch manager in Leeds can mentor a junior manager in Bristol. In my foundation, we've taken this to a global scale, connecting women entrepreneurs in developing countries and emerging markets like India, Kenya, Mexico and Lebanon to male and female mentors in the UK and beyond. We have a cupcake business owner in Malaysia being mentored by an operations manager in Essex, a sales executive in New York mentoring a fashion designer in Swaziland.

But it can also be as simple as having a few encouraging words with someone in your office, actively taking an interest, praising their skills to colleagues and management. It doesn't have to be time consuming - in my foundation's own mentoring programme, we just ask for two hours a month of our mentors' time - and it can change a life. As mentoring becomes more widespread, it can help level the playing field. I wouldn't have got as far in my legal career without mentors and that's why I'm so passionate about it.

As Madeleine Albright said, "There is a special place in hell for women who don't help other women." It doesn't make sense. Let's get a bit more collaborative and start giving each other a hand up.

Cherie Blair will be speaking about mentoring at the next Stylist Magazine Stylist Network Event on 4 February. For more on the Cherie Blair Foundation for Women's mentoring programme: www.cherieblairfoundation.org

This article originally appeared in the Mail on Sunday.

Follow Cherie Blair on Twitter: www.twitter.com/CherieBlairFndn