Once, I was walking down the street when a group of men came up behind me. I didn't turn around. There was plenty of room on the pavement for them to pass by. But they didn't. They stopped behind me and one, suddenly, roughly and completely out of the blue, grabbed my jeans-clad bottom from behind and squeezed, pushing his fingers forwards and upwards towards my crotch.

I'd like to say that I screamed; that I put him in his place there and then and articulately delivered a cutting speech that shamed him into apologising. I'd like to say that I said anything at all. But I didn't. I gasped, I froze, and I felt the blood rush to my face in mortification. Then I stood there, silently, as they walked away laughing.

The Everyday Sexism Project was designed to document instances of normalised, everyday sexism experienced by women worldwide to prove the enormous scale of the problem. But since it launched five months ago, we have received hundreds of reports of women being groped, grabbed, manhandled, slapped, tweaked, pinched, stroked and smacked in public, usually by complete strangers. The area of focus is almost always the breasts, the bottom or the thighs - sensitive, sexual, intimate regions of the body. And the tone of the reports usually mirrors my own experience almost exactly in that the victim describes an overwhelming sense of powerlessness, fear, shame and embarrassment:

"First job, first day. Age 18. Barmaid. Men lifted top up revealing my bra to pub. I walked out in tears. Never went back."

"Dancing in crowd at festival, guy slaps arse. Crowd had thinned out, conscious everyone saw, too embarrassed to even react."

"Younger sister and I were groped on a water slide by a man when about eight and nine years old. Too ashamed to tell mum and dad at the bottom."

"Twice in pubs in Newcastle. Full on arse grab while leaning against the bar. So upset both times I had to go home."

"Aged 14 had bum slapped by man in supermarket. Was too scared to enter said supermarket again until very recently (I'm 19)."

"Random grabbed my breasts in the street in broad daylight. Too shocked to even scream."

What is even more shocking is the overwhelming frequency of these incidents. When I asked on Twitter how often women experienced unwanted touching, groping or grabbing, the responses were alarming:

"At least once a week and often much more, regardless of what I wear, where I am, how I behave. Usually breasts, hips, ass."

"I've had a man put hand up my skirt while walking behind me up stairs out of tube station, boobs grabbed while on nights out. Also had bottom slapped by boss while working in HR (!) And flashed at several times over the years while out and about."

"It happened quite often, at least every month when I was a teen or in my twenties, but still too often nowadays that a guy would grab for my bottom, breasts or flash/masturbate in front of me."

This is not a single, horrible event women suffer once in their lifetime - it is becoming an epidemic - a normalised occupational hazard of being a woman. As one contributor wryly put it, "I committed the terrible crime of being female and out in public on my own."

But the real crime is being committed by the people who are touching these women against their will in a sexual way. UK legislation on sexual assault is very clear:

A person (A) commits an offence if--
(a) he intentionally touches another person (B),
(b) the touching is sexual,
(c) B does not consent to the touching, and
(d)A does not reasonably believe that B consents

Under this definition, every one of the hundreds of women who have reported such experiences to our project was the victim of sexual assault - a crime which, under UK law, carries a maximum ten year prison sentence.

Yet we are living in a society that not only downplays and accepts this crime, but deliberately normalises it, telling women not to overreact, not to make a fuss out of nothing, or even to be glad of the attention. It is only when you really spell out the definition of the crime that the realisation begins to dawn, even for many of the victims. One woman wrote to us today to say:

"Never thought about it before, but have now worked out that I've been sexually assaulted at least five times."

Others testified to the normalisation of a crime that is becoming so common and accepted that it is neither reported nor taken seriously:

"It seemed minor, scared the hell out of me though. I was crying by the time I got home."

"One of the blokes put his hand up my skirt and grabbed my crotch! Groping is too common on a night out! Never gets reported because it happens so often!"

"On tube man "fell" onto me, in clubs/pubs a lot... whilst pregnant was the most upsetting for some reason. Report to whom..?"

And of course this lack of report and convictions leads to a culture of impunity, with myriad stories sent in to our website painting a clear picture of a society in which many feel it is their right to sexually assault a woman in public without shame or fear of reprisal.

"At 17 years old and short, big bloke in group at pub grabbed my bum. Told him to get lost, he did it again..."

"Friend had man walk up to her in the street, tweak her nipple, then walk off."

"Man put his hand up my skirt when walking down the road. Shouted at him that he had no right to touch me. He seemed shocked."

"First day of work on packed tube, guy in suit put his hand between my legs, when I loudly complained he said 'stupid dyke'."

"On Tuesday, out for a run. A man (not a runner) ran towards directly me and literally landed with his hands on my breasts."

"On my street a man walking the other way reaches out & grabs my boob. I shout noise & try to slap him. He just GRINS at me."

"I was on my bike at the traffic lights and a man got out his car to grope me."

Indeed the overwhelming message being sent is not only one of impunity for perpetrators, but that the victims of sexual assault are not permitted to react - there is a strong sense of public complicity in the treatment of women as objects to be touched and grabbed at will - and a feeling of oppression of women who dare to speak up about it:

"A man put his hand up my skirt on a night bus home, I shouted he was a pervert, man behind me told me to be quiet."

"Was reporting from court when a man grabbed my bum. Clerk told me I had 'got off lightly' and not to bother reporting it."

"When I try to hit him or shout at him, [he] react[s] like I'm the one who's crazy."

"I got sexually assaulted at bus station, police involved, when I got home, Dad said 'What d'ya expect wearing a short skirt?'"

"Walking home, guy stopped me, grabbed my breasts and tried to kiss me. I yelled at him, he looked shocked and annoyed. I ran."

"Walking down the street with my dad age 12... got my bum slapped...reported it- to no avail."

"Police took my statement then said maybe I was catching attention because I was wearing a short summer frock."

"When I told three police officers... and pointed out harassment was illegal under the Harassment Act and Sexual Offences Act, one officer replied, 'Oh, you're getting technical on us are you?'"

What does it say to a woman if she is sexually assaulted in broad daylight or in a public place and the people around her avert their eyes, or tut at her for daring to make a noise about it, or accuse her of inviting the attention because of her clothing or her behaviour? The overwhelming message is that women should expect this treatment- that the fact it is a crime is irrelevant, they must come to expect it as a part of their lot. Crucially, it sends the message that both the responsibility for the crime itself and the responsibility for avoiding it is somehow theirs. And the language of the stories we receive reflects this sad normalisation:

"Worst was a whole crotch grab. Sad thing is I remember as it wasn't 'just' a bum pinch which would be more normal!"

"Had my ass slapped by some guy on a bike while walking down the street and talking on the phone. Now I avoid walking alone."

"At school I used to get my bum pinched on a regular basis. It's one of the worst ways to be groped because you can't see it coming and avoid it"

We live in a society where women are not only reporting being victims to a crime that carries a ten year prison sentence on a weekly basis, with no repercussions, but discussing it in such normalised terms that they casually differentiate between the various "ways to be groped".

The reason I didn't react when I was sexually assaulted in the street was because of the overwhelming awareness, gently, insidiously, gradually impressed upon us all, that this crime is not taken seriously. I knew with absolute certainty that to use the label, 'sexual assault', which is entirely the correct definition according to UK law, would brand me overreacting or attention seeking or worse. Even inside my own head the term felt like an exaggeration. Figures suggest that around 400,000 women are sexually assaulted every year in the UK. But of the hundreds who have testified to it on our project website, only a handful said they ever reported it, suggesting that the real figure is likely to be far, far higher. I have never, ever said that I was sexually assaulted. The words feel alien to me. It feels embarrassing, like trying to claim something more of a big deal happened. The hundreds of women who wrote to tell us about their own experiences of sexual assault have probably never said it either. We have created a social disconnect between the crime and its perception that is so strong that even its own victims deny it. Which is, of course, the ideal environment for such a crime to flourish?

So if we publicly normalise and downplay this crime to such an extent, what is the knock-on effect? Does every crime against women slip one rung further down the ladder, with rape also being taken less seriously, doubted and discussed and analysed in the public arena as if it were a matter of opinion rather than an indisputable crime? Recent events would certainly seem to suggest that that is precisely the case. And in such a paradigm, what happens to the offences of sexual harassment that over four thousand entries have reported to our website; that hundreds of women from all over the world are writing to tell us that they suffer daily? Well they slip off the bottom of the ladder altogether.

Follow Laura Bates on Twitter: www.twitter.com/EverydaySexism