Author Marianne Levy's 50-mile school journeys were a series of melodramas

'I only like him about 30 per cent now. Which is way down from before, when I liked him 100 per cent."

"That's so many per cent, Ruby."

"I know."

Ever wondered what happens after you've dropped your teenager at the bus stop? As the nation's children returned for the January term, I decided to find out, and now I'm sitting on the back seat with the 4pm crowd, right between Ruby and her friend, my head swivelling to catch their words over the growl of the engine. I'm the most obvious undercover reporter ever. But I'm not wearing school uniform, and so, as far as they're concerned, I'm completely invisible.

A lot has happened in the couple of decades since I took the bus to school. But it's good to know that some things haven't really changed.

Though I am currently juddering across north London, my journey once took me from Chelmsford to Colchester and back. It was a 50-mile round trip. And it made Lord of the Flies look like a spa break. So when I was searching for a scary landscape into which to plunge the heroine of my new teen-fiction novel, there was no need to conjure up a vampire-ridden dystopia; I just had to travel back 20 years in my own head.

The discussion turns to whether or not Ali's shoes are Air Max ("Obviously they are not," says Ruby), and as we turn a corner, I stagger down towards the front to check in on a pair of tiny boys, apple-cheeked angels in blazers. The more cherubic of the two is spewing forth a stream of swearwords that would shame Irvine Welsh. His friend responds by bashing him over the head with a violin case. It's all reassuringly familiar, although I'm worried for the violin.

In my days of getting the bus, I wouldn't have given the safety of musical instruments a second thought; my entire focus was on self-preservation. Culled from four very different schools and trapped together for around 15 hours every week, we formed a strange, uneasy society. There was the chubby boy, whose life we made a living hell, until he returned one September having apparently grown 4ft in six weeks. The sad-eyed wraith who did two hours' high-diving practice before arriving at the bus stop, smelling faintly of chlorine, a little after 7am. And a girl who welcomed me on my first day by asking, "Have you had an orgasm yet?" We were 11 years old.

There were adults, of course, but they ignored us. The bus driver, occasionally called upon to intervene after a particularly brutal fight, would inevitably refuse to get involved, saying gloomily (and probably correctly), "I'm not paid enough for this."

And with all regular rules of behaviour suspended, things became very odd indeed. I have a vague memory of two of the boys telling us they were going to hold up an off-licence. That night, they did. We never saw them again. After a week or two, it was as if they'd never existed.

But I do recall with perfect clarity one girl setting light to a strand of her hair, how it burnt up with a speed that left us all in shock. Then there was the day I explained periods to a group of year seven boys, my description of the inner workings of the female body holding them in rapt, fascinated silence.

open image in gallery

There were moments of genuine danger, too: the night my friend crossed in front of the bus and bounced off a Volvo through a lane of fast traffic; the time the sunroof caught a branch and flew off, leaving a square of night sky pouring cold air down on to our surprised heads.

Whole lifetimes' worth of social interaction could be condensed into a single journey; wars fought, bonds forged and loves lost while the double-decker idled in traffic on the Kelvedon slip road. Take Orgasm Girl: I loathed her, was terrified of her, yet wanted to be her and couldn't wait to see what she did next. In return, she ridiculed me, pulled my hair, sat next to me and made sure to keep me up to date on her many, many sexual conquests. Even I didn't understand our relationship, and I was there.

Do I miss it? Maybe, just a little. It was exhausting, the constant attack and defence, the emotional energy we'd expend on the most trivial arguments, the way any foodstuff might be turned into a missile. But then there were the frosty mornings when we'd send our breath up in warm white plumes and pretend we were holding cigarettes, the secrets shared over a flaking Curly Wurly as the top deck emptied, the friendships so intense they burned.

I would love to go back, to relive those days, but some years ago the council finally decided to run an official Chelmsford-Colchester school bus, closed to outsiders. Outsiders like… me.

But really, as an adult, that world had already shut its hydraulic doors. Back in London, the girls barge past me, and, as though to drive the point home, one actually stands on my foot as she reaches for the bell.

"See ya, Rubes," says her friend, swinging off on to the pavement. And Ruby settles down into her seat, pops her headphones into her ears, and flashes me a tiny, satisfied smile.

'Accidental Superstar', by Marianne Levy (£6.99, Pan Macmillan), is out now