This year marks the 25th anniversary of the world wide web, and I wonder whether its inventor, Tim Berners-Lee, would still have given it away had he known where it would be now. Had he foreseen Google and Facebook and Twitter, the conquest of web porn and the normalisation among teen-agers of misogyny and sodomy, the endless harvesting and mining of data, the surveillance, the cruelty and vulgarity and invasive crassness, the commercialisation of everything — would he still have said, ‘Have it for free, in the common good’?

That’s a question that only he can answer. But the great fascination of the web lies in the near-asymptotic rate at which it has grown, not only in scope but in its domination of our lives. It is like a speeded-up version of cultural and commercial evolution — and one which no one could have predicted. Even web billionaires have only got rich by guessing one tiny element of its potential, and making it come true.

Jamie Bartlett’s interesting approach is to look at the web from inside out. ‘The Dark Net’ of his title refers to the submerged, anonymous, unaccountable — and, being unknown, uncountable — users accessing the web via the TOR network. The acronym stands for ‘The Onion Router’, a way of navigating the internet by multiple layers of anonymously relayed data. And the significance of TOR, and the ‘hidden’ web it gives access to, is that it is still largely private. ‘Privacy’ in this case doesn’t mean ‘exclusive’ or ‘members only’. You don’t have to be put up for TOR. You can’t be blackballed. But nor can you be identified or traced.

Bartlett works for the think tank Demos, where he specialises in the political and cultural effects of social media — the stuff that governmental and commercial agencies are desperate to get hold of, and are pretty successful in doing so. But the dark net is still largely beyond their reach. Bartlett anatomises the usual bogeymen and demonstrates that they’re real.

There are paedophiles. There are terrorists. There are online drug-dealers with their own equivalent of Amazon, complete with customer ratings. There are teenage girls offering their bodies to what one imagines as the spod-like sweaty gaze of inadequate men. And there are moral husks, pustular with inchoate rage, exposing the identity — ‘doxxing’ — of those girls to their parents, friends, schoolfellows and, of course, posterity — because nothing ever, ever goes away on the web. There are pro-suicide sites, pro-anorexia sites, copyright-theft sites, sites devoted to incivility, cruelty and lives lived in a moral vacuum.

And in one sense we should be thankful for the dark net’s existence. What neither Berners-Lee nor anyone else could have foreseen was the ownership of the web, and thus of much of our social existence. It is, of course, an adulterer’s charter. There was a time, 25 years ago and before, when communications were private, but announced themselves. The letter-box clattered, the postman knocked, the telephone rang. You may not have been able to read the telegram, but you saw the telegram boy and you knew who the telegram was for. Outside the house (and the GPO) no one else knew anything.

Now, communication is, by default, silent. No more hastily dropped calls or letters shoved under the sofa cushion. Your wife could right now be sending illicit love-texts sitting on the edge of the bath. The only giveaways are post-facto itemised bills or the (easily cleared) recent calls list. The only exception is the foreign ringtone on your husband’s mobile when he’s told you he’s going to Glasgow. Otherwise, computers, smartphones, iPads, passwords, fingerprint recognition and lock-screens ensure all communication arrives or leaves unannounced.

But what the household doesn’t know, governments, Google, Facebook and Twitter do know, and they mine it. The web which, in our hippy, often uncouth way, we once saw as a guarantee of free communication, has become the means by which our souls are rented out to the highest bidder. And the bidder is advertising. Advertising rules the online world. Not, however, on the dark web. There you are not tracked, packaged, sold off like so many dodgy securitised debt packages in the hope of breaking better-than-even. There you can do what you like.

And what we like seems to be pretty dark itself. Astonishingly, there are many who are surprised. But in their surprise they seem to draw the wrong conclusion. Like old-style fundamentalists, they believe that anonymity is the thing which makes our inherent darkness visible. Without the restraint of identification, we behave like mad pigs — just scan the ‘Have Your Say’ sections of any newspaper. But — as H.G. Wells argued in The Invisible Man — isn’t it equally, or more likely that we behave like mad pigs not because we are inherently piggish but because our invisibility has itself driven us mad?

The Dark Net is, for anyone engaged with the web and the effects it is having on our culture, necessary reading, not least because it reveals just how much of the web is in reality the search engine we use — particularly if that search engine (like Google) is carefully engineered to confirm our biases in an eerie foreplay to get us ready for the advertising industry. That, and the fact that most people never go beyond page three of their Google results, means that what we believe is the world wide web is no such thing: it’s a tiny, balkanised and personalised millimetre of one thin strand of the webbing. We are cordoned off among like-minded people without even realising it. Google, which handles about 70 per cent of internet searches, is like one of those old-fashioned librarians suggesting to readers things he knows they’ll like. In comparison, the lawless, vulgar, often cruel, frequently repugnant borderlands of the dark web stand as a sort of corrective balance.

Where will it end? I haven’t the faintest idea, and neither have you. But Bartlett’s trip over the frontiers into the web where the law’s writ does not run is as necessary as a flashlight in a dark, dark cellar.