As breeding grounds for talent go, it could give the country's top girls' schools a run for their money, counting JK Rowling, Dame Kelly Holmes and Emma Thompson among its former members.
Unlike those venerable institutions, however, the organisation that has helped to mould the characters of some of the nation's most successful women is often dismissed as a harmless pastime for middle-class white girls. Now, as the Girlguiding movement approaches its centenary, the organisation is keen to ditch its twee image and embrace the modern world.
The organisation has spent the past two years trying to boost its 600,000-strong membership – and drag the organisation firmly into the 21st century - using an outreach programme called the "Switch" project to recruit young women who would never normally set foot in a Girl Guide meeting; everyone from teenage mothers to girls from conservative Muslim families.
"We have more than half a million members, but there will be 11 million children in the country next year, so obviously we could be serving more girls," said Denise King, chief executive of Girlguiding UK.
The traditional "character-building" activities for which the movement was famed, such as learning to tie knots, put up tents and administer first aid, have been expanded in order to appeal to girls with different interests.
A group of young mums in Nelson, Norfolk learned to cook cheap meals on a budget, complete an NSPCC course on keeping children safe, and were taught how to plan affordable day trips for youngsters. Even the classic Girl Guide badges – which for years were proudly displayed on blue sashes, after being painstakingly sewn on by diligent mothers– have been expanded and updated to cover more political topics.
At some groups with a lot of Muslim members, girls work towards the new "Right To" badge, which teaches them about their right to be heard, to express their feelings and to worship.
"Usually we don't get the opportunity to join groups, so it is nice to be able to hang out with other girls without my parents worrying about boys being there" said 15-year-old Amani Khan, who attends a Middlesbrough Guide group. "They are generally quite protective, and it was nice to be able to make new friends and build my self-confidence."
Creating a female-only space in which girls can feel comfortable trying new things has always been one of the main objectives of the Guide movement.
Next month 7,000 Girl Guides will gather at Crystal Palace, south London, the spot where in 1909 girls in makeshift uniforms stormed a Boy Scout meeting and demanded that a group be created for them, to celebrate the organisation.
When Robert Baden-Powell, who went on to found the Girl Guides, wrote Scouting for Boys in 1908, he noted that: "Girls as well as boys may well learn scouting when young, and so be able to do useful work in the world when they are older." With a quick survey of former Guides turning up an Olympic gold medallist, a leading politician, an award-winning actress and a best-selling author, it looks as if he may well have been on to something.
Silverton, who was taught to target-shoot from a young age and got her first Magnum at 14, said that attending Girl Guides in her native Essex allowed her to indulge in more boyish pastimes. "I was a Girl Guide and head girl. I was a tomboy then and in many respects still feel like one now."
For Reader, attending Girl Guides highlighted the problem of sectarianism: "In heavily segregated Glasgow during the 70s, when I was growing up, we had two separate Guides and Brownie clubs. Me, being Catholic by birth, should have been going to the Catholic Girl Guides, but I was in the Protestant club because my best friend Caroline Nicholson was Protestant and was in the Protestant Brownies, and I went along with her. It felt fantastic, daring and exotic. One of the main things I think it taught me, inadvertently, was how ridiculous segregation was."
The former Girl Guide and Oscar-winning actress believes that through the organisation "girls and young women can gain the confidence to be equal partners and to make informed, responsible choices about their lives". Thompson is now working with the Guides again, on a project which encourages them to become "Climate Champions", reducing carbon emissions by advocating solar panels, switching off appliances and properly insulating homes. "Becoming a Climate Champion will enable girls and young women to take effective action on climate change – the biggest challenge the planet faces," she says.
Stoddart, one of Britain's most successful racing drivers, admits to being hyper-competitive on the track, but says that attending Guides made her realise "the importance of teamwork and motivation to achieve what you want".
When the stand-up comedian's father was branded "a traitor to the revolution" in Iran and the family fled to London, Khorsandi threw herself into all things English, including Guiding. Khorsandi, whose book A Beginner's Guide to Acting English was published in July, says the organisation taught her "compassion and kindness".
Dame Kelly Holmes
The Olympic champion says attending Girl Guide meetings in Kent taught her to "be the best you can be". It seems that the gold medal winner is now inspiring others to reach their full potential, with a recent survey of Girl Guides revealing that 86 per cent of them believe Dame Kelly to be the country's best female role model.
The Harry Potter author, who attended Brownies and Guides in Scotland, thinks Hermione Granger would make a good Guide: "I can easily imagine her in the Guides, given that she's resourceful, highly motivated and eager to learn. She might be a little over-competitive when it came to badges, though." She says her proudest guiding memory was bagging her First Aid badge: "I've never needed to make a sling since, but I'm on constant standby."
The MP says one of her favourite guiding memories was "learning to knit on four needles". "When I think now about the angst young women go through about their bodies and their clothing, looking back it seems like a lovely time of innocent pleasure."
Dame Tanni Grey-Thompson
"My experience in the Brownies was very much a 'can do' attitude. No sitting around and moaning. Just get on with it. Sometimes people seem to be a bit wimpy these days. Lots of stuff we did probably wasn't very safe – we had knives and scissors and candles. But, you know, nobody got hurt."
While the Ugly Betty actress may call Hollywood home now, her experience of Girlguiding in Scotland was a distinctly rural experience. "I was brought up in Annan in Dumfriesshire which is a pretty big farming area, and although I was not brought up on a farm I gained my milkmaid badge, which I was exceptionally proud of." She says the best thing about Guides was "being part of a team and working together alongside other people, and not being afraid to try new challenging things that you may not have thought about yourself".