Tomorrow, the House of Lords will debate Labour's proposed amendment to the children and families bill, a piece of legislation that would result in compulsory sex and relationships education being taught in all English schools. It is, I believe, a matter of some urgency, not only because Labour says that violence in teenage relationships is increasing, but also because of the many ways in which online porn's dominance is affecting sexual relationships and behaviour in the real world. You might say that this is not the case, of course. The links have not yet been convincingly drawn, and until they are, it's my word against yours. So here they are: my words.

In the last couple of years I have spent much of my time talking to young women, about their hopes for the future, about the things that make them angry or sad or frustrated, and porn is something that crops up again and again. "I'm so sick of it," some girl or other will rage, after a talk, a large glass of warm white wine in her hand, and she'll tell her story. It will vary in the details, but the bare bones are always the same. She'll have been asked to do something in bed that she was uncomfortable with, and she won't have had the language or the confidence to refuse. This is if the guy's especially polite, by the way. Sometimes they don't bother to ask.

"Do you think porn influences the way men behave towards you?" I'll ask. "Absolutely," they always say. I have come to realise that having concerns about pornography is not merely an attitude symptomatic of a kind of puritan, conservative hysteria; it's something that young women are worrying about on a regular basis, because they are living it. Sexually active, bright, independent young women, doing things they don't want to do in bed, and then crying about it afterwards.

"It's clear that porn is having an effect," says one. "I mean, when a guy asks to come in your hair, he's not thought that up by himself. He's got that from somewhere." Last year, HBO's Girls, a series followed by its young female audience with a kind of religious fervour, contained a scene where the male character has his girlfriend crawl along the floor, before he ejaculated on her back. "Been there," said a friend, while watching it.

It's all anecdotal, of course, which is why we need a massive, nationwide investigation, and we need it right now. But even more urgently, we need sex education. Proper, cohesive, sex education. Because at the moment, the only place young people can easily learn about sex is on the internet, and internet pornography does skirt around certain sexual essentials. Consent, for instance, tends to be a grey area.

Here is why we need sex education: we need sex education because (some) men are asking for anal sex on the first date. This is fact. If you do not believe it, then I'm afraid, you simply haven't spoken to enough women in their 20s. We need sex education, because (some) men seem to think sex ends with him ejaculating on your breasts, or in your hair, or in your face. We need sex education because of a practice called "seagulling", a boarding school import (what else?) that has spread to some university halls of residence. It involves a group of guys standing outside a mate's door while he has sex with a girl, and then bursting in and ejaculating over her, all at once. We need sex education because women are telling me they're fed up of being told they're a "bitch" or a "dirty little whore" or a "slut" in bed. That they need to be "violated" or "ruined". We need sex education because I have lost count of the number of times that young women have told me that their boyfriend or sex partner has placed his hands around their neck and tried to choke them during sex.

Of course, you may be a woman, and you may enjoy all of these things and more. Human sexuality is varied and fluid and experimentation is to be encouraged. The feminists of the 1960s held that sexual freedom was key to the liberation of women. I believe that. But it's clear to anyone who's out there sleeping with men, the sexual landscape has changed, and under no circumstances can it be called freedom. So often these experiences are recounted with a laugh, or a derisive snort: these men (not all men, it's never all men, but it's enough of them) are the butt of a joke. Outside the bedroom, their female sexual partners look down on them and their "weird" urges and requests; inside, they are expected to submit.

Sex education is not simply about teaching women how to say "no" when men are taught to say "yes", it's about showing both genders what a healthy relationship looks like. It's about teaching them how to recognise consent, and that consent can be withdrawn at any time, and that it is not, always, verbal. Some interviews with young men have revealed much confusion on this point – porn has taught some of them that resistance is a kind of foreplay: it isn't. Good sex education means having someone explain this to them without blushing or stuttering, in language that they understand, without the need for a cartoon of a dancing condom. Good sex education does not stop at the mechanics.

Porn in and of itself is not the problem; after all, it's just people, having sex, on a screen, sometimes not especially convincingly. No, porn is not the problem: it's the complete and utter absence of any other narrative that is, and the disappointing failure of our government to provide one.