For me, being a Guide was not a brief flirtation. Almost half of all girls in the UK have some experience of guiding, and many, like me graduate from the Brownies and reach the dizzy heights of patrol leader. I was a dab hand at semaphore – a useful skill in court – and I threw myself with enthusiasm into our camping trips and usually into any stream we passed. I can still summon up my campfire songs.

We took part in local community work, particularly helping out younger children and the elderly. From time to time, we reflected on the international aspect of guiding. We knew we were part of something big. But guiding to me as a girl was about fun and friends. It is only later, learning of the limited power so many girls and young women have over their lives, that I have come to realise what an inspirational force for good it is in the world.

Guiding is the biggest female-only movement on the planet, with over 10 million members in 145 countries from Armenia to Zimbabwe. It provides a fantastic opportunity for girls and young women to learn in supportive surroundings the leadership skills and confidence they need for later life. In many places, only guiding offers girls a place to voice their opinions in cultures where women are often treated as second-class citizens. It also provides a safe female-only environment where girls, at least for a time, are allowed to be just girls.

Boys are much likely to be educated. In many societies, they escape the household duties. It is their sisters who are expected to help out, whether by fetching water, cleaning, cooking or looking after younger children. They find themselves catapulted into the responsibilities of adulthood just at a critical time in their personal and social development. With no formal structures, in many countries, to support young women, it is reassuring to know that guiding is actively working right across the developing world.

Over the years, I have met Guides from many countries. Whether they live in Canada or Rwanda, Australia or Uganda, the shared commitment to helping girls fulfil their potential, whatever the circumstances, is evident. Each group was impressive, committed to making the most of their potential, interested in the world outside their communities and borders.

It is this interest which is the focus of guiding this weekend, when guides of all backgrounds, faiths and cultures come together to celebrate World Thinking Day. It underlines just how guiding has grown up. In the UK alone, nine One World One Beat events will bring together more than 18,500 Girlguiding UK members, exploring through world music, drama and dance the issues girls and young women face in developing countries.

In South Africa, in the worst days of apartheid, the Guides maintained mix-race troops. Guiding is also prominent in many countries in HIV/Aids education and helping remove the stigma from the disease. There has been real progress in the lives of many girls and women since guiding was founded in the UK a century ago this year, but in a world in which women are still twice as likely as men to live in poverty and two in three illiterate adults are women, there is a huge amount more to do.

Providing girls across the world with the confidence and the skills to make their own decisions, stand up and take action should be a global ambition for us all. As a proud, if accident-prone former Guide, I salute an organisation which celebrates its centenary this year in fantastic health.

Cherie Blair is Founder of the Cherie Blair Foundation for Women www.cherieblairfoundation.org