There’s nothing exciting about clearing out all kinds of junk that’s been festering in your cupboards for decades, but occasionally you come across a hidden gem that you’d forgotten ever existed, and this happened to me last week when I found a letter I’d been hanging onto for the best part of 18 years.

My best friend Samantha (aka Butty - best you don’t ask) had written it for me in primary school as I went on holiday to stop me getting bored on the plane. It was a tradition that we kept up every time either of us went away, we always had to write each other a letter, regardless of which one of us was going away. The stipulation was that it had to be at least 10 pages long and feature quizzes, games and reams of gossip to keep each other occupied for hours.

As I read the letter, which referenced the things that used to dominate our lives at the time such as the Spice Girls, Top of the Pops and Peter Andre, it made me think about female friendship and how far Butty and I have come since she wrote that letter when we were a just couple of nine-year-olds whose only main concerns in life were convincing our parents to allow us to stay up past 9pm and trying to stop the teachers confiscating our friendship bracelets.

Friendships between women are deep and complex, particularly in the adolescent years when you’re a riot of hormones and insecurities, seething with resentment, unspoken competition and simmering jealousies, and boy was there a lot of that for me and Butty in our teens.

For the majority of our school years we were engaged in subtle, unspoken battle with each other; for popularity, whose English coursework the teacher would prefer - even for who was better at ‘plucking’ in our ill-fated violin lessons.

Female friendship is tested by time - it either strengthens it or splits it, and since I first met Butty 24 years ago, I think it’s fair to say our friendship has stood the test of time. Out of all my wonderful friends, which include some men, she’s stuck around the longest, and though of course it’s not been plain sailing by any means, there’s not much we haven’t been through together.

Death, divorce, betrayal and distance - there have certainly been challenges but at the end of the day, she’s the person I trusted to dye my hair over the sink aged 14, and the only one in the world who knew the special code names we had for the boys we secretly fancied. She’s also the only one who can speak the ridiculous language we made up in the canteen queue in 1998.

As we have grown into women our friendship has also grown. She’s the person who listens to my repetitive work and relationship dramas, over and over again, giving me advice, despite the fact she’s not being paid £75 an hour. She’s also the same person who I know would pick me up if my car breaks down and the one who won’t judge me for demolishing an entire bag of doughnuts and pack of biscuits - she’ll sit and join in.

As teenagers

So, no matter how stressed out I might feel, talking to Butty really does end up making me feel better.

Ruthellen Josselson, who co-wrote Best Friends: The Pleasures and Perils of Girls’ and Women’s Friendships, says women can be an incredible source of strength to each other. “We nurture one another and we need to have unpressured space in which we can do the special kind of talk that women do when they’re with other women. It’s a very healing experience,” she explains.

In films and TV shows, female friendships are often portrayed in romanticised and unrealistic manners - everything’s rosy and uncomplicated. But the truth is, they ARE complicated, and can often be marked by competition, resentment and disappointment as well as the good stuff.

Yet female friendship can be one of the strongest human bonds. A good one consists of an ongoing loyalty that can rival marriage and blood ties in importance and value.

Women’s friendships are different to men’s, in that men communicate in the language of information, and women in the language of feelings. The dynamics are different.

Falling out with a good friend can be just as agonizing as any romantic relationship, but if you are lucky enough to go the distance, it’s so rewarding.

At the risk of sounding cheesy, (because I really don’t like mush) my friendship with Butty is one of the things I value most in my life.

We don’t have to speak to each other every day, because we have our own lives, and we both have demanding jobs.

A few days may go by when I suddenly realise I haven’t spoken to her for a few days.

But it doesn’t matter, because as soon as we do, it’s exactly how it’s always been, and the same as it was when she lived at the other end of the country for eight years.

We shared the passage into adulthood and as she once described in a birthday card to me, we’ll undoubtedly be exactly the same when we’re queuing up at the post office for our pensions.

Bring it on.