Ten years ago this month, millions of people all over the world marched against the war in Iraq – and were ignored. I was one of them. For me, at the age of 16, there were a lot of firsts on 15 February 2003: first truancy, first solo trip to London, first time seeing democracy rudely circumvented.

Tony Blair’s decision to take Britain into the Americans’ war in Iraq was an immediate, material calamity for millions of people in the Middle East. I’m writing here, though, about the effect of that decision on the generation in the west who were children then and are adults now. For us, the sense of betrayal was life-changing. We had thought that millions of people making their voices heard would be enough and we were wrong.

I wasn’t an activist at the time. I was just a schoolgirl overawed by the sheer scale of my own powerlessnesss. The bus to London from the centre of town left early in the morning and I bagged a seat at the back alongside some older students who chatted about the first Gulf war and the international oil lobby. One of them, I remember, was carrying a handmade placard with a picture of a woman’s pubic triangle luxuriously adorned with real, glued-on human hair and the legend “The Only Bush I’d Trust Is My Own”. Upon being asked the obvious question, she indicated the shy, smiling young man beside her and told us: “Armpit hair.”

As London began to materialise out of its dowdy, drawn-out suburbs, we had no conception of the scale of the organisation and planning involved to get two million people on to the streets. When we got off the bus at Embankment, the roadsides were crammed with buses, people surging along the pavement, joining the hundreds pouring into the road, the whistle-sellers and the newspaper hawkers directing us. Under the bridges by the river, the people moved like a flood. I shinned up a set of traffic lights to get a better look. Tens of thousands of banners and placards, most of them churned out of the same Stop the War press and bearing the legends “No” and “Not in My Name”, moving with slow certainty towards Westminster. From above, all of those cardboard squares seemed to tessellate and resolve into a larger picture – No. No. No. No. No.

It was the first time I remember feeling part of something larger than myself. It was only later, after the war and the next six years of progressive assault on civil liberties had broken any faith I or my schoolmates might have had in the Labour Party, that I learned about the endless arguments that went on behind the scenes. At the time I had no idea of the factional squabbling that prevented that march from becoming the powerful people’s movement it might have been. I don’t remember the presence of union members and socialist parties as vividly as I remember the performance artists with their creepy, bloodypaint- spattered masks, the kids strapped on their parents’ backs, the elderly couples with their Thermos flasks and sandwiches wrapped in foil.

It was a very British protest: polite, resentful and passive-aggressive. One got the sense that if Tony Blair had shown up, he’d have been subject to a mass blanking. There was a muted menace to the mood, chants that would flare up and then die down, some of them endearingly altered versions of current chart hits (“Who let the bombs drop? Bush, Bush and Blair!”). Most of all, there were the whistles, shrill and incoherent and frustrated, like 10,000 PE teachers on the move, a notion that still crops up in my nightmares.

What changed in 2003 was that millions of ordinary citizens around the world finally understood that the game was rigged, because only a few weeks after that march the US and its allies went to war anyway. The people had withdrawn their consent, loudly and peacefully and in numbers too big to ignore, and they had been rebuffed with hardly a second thought. Representative democracy had failed to represent.

“Not in My Name” felt, even at the time, like a slogan of last resort, as if we had already accepted, on some level, that war was going to happen and the most we could do was tut disapprovingly. The terrible thing about protest is that when it remains satisfied with expressing distaste for the status quo, the status quo is quite happy to proceed as planned. Two million people went home that day feeling they’d at least made their objections felt, but it turned out not to be enough. In the end, it was in our name.

I have no doubt that, a decade from now, people in their mid-twenties will speak of the student riots of 2010-2011 with the same sad sense of lessons learned. At Millbank, when 4,000 students and schoolchildren smashed up the entrance to the Conservative Party headquarters and held an impromptu rave in the lobby, several young people mentioned the Stop the War march of 2003, how all that passive, peaceful shuffling from one rally point to another had failed to achieve anything concrete.

My generation’s lack of faith in the political process has often been mistaken for apathy. It is only now, with ordinary people across the world putting their energies into movements that bypass mainstream politics, that the betrayal of Bush and Blair’s wars is beginning to be understood. We have known since we were at school that it’s not enough simply to make our voices heard. We have to make sure that we are listened to – and we’re still working out how to do that.

Editor's note: This piece originally stated that Nato went to war in Iraq. The error has been corrected.