THERE are thousands of books about the internet and its impact on society, but this is the only one you really need. It’s published at exactly the right moment too, while the revelations about Cambridge Analytica, and the misuse of our data, are very much in the public mind. It is compelling also because written by a classic poacher-turned-gamekeeper.

Jamie Bartlett is a former digital evangelist who's proselytised all things web for the left-leaning think-tank Demos since the early noughties. “But over the years”, he writes, “my optimism drifted into realism, then morphed into nervousness. Now it is approaching mild panic”. He realised that the technology he believed would promote an informed, interactive democracy is doing the reverse: undermining democracy by creating what he calls digital “tribalism”. This is most apparent in the righteous Twitter mobs who roam the internet looking for reasons to be offended, and people to scold. Rational debate is being replaced by what Bartlett calls “a strange performative politics”, in which virtue-signalling to the tribe supplants fact or argument.

Simultaneously, having lost control of our data, we are putting immense power in the hands of a digital elite. The titans of tech, like Facebook's Mark Zuckerberg, are themselves only dimly aware of how their algorithms actually work at a societal level. Regulation must come, since these “platforms” are now the biggest publishers in the world, yet accept no responsibility for what they publish, be it fake news, sadistic Peppa Pig videos, racist hate speak or rampant conspiracy theories. However, if we hand this technology of surveillance and control to the state, how might government misuse it?

Panic indeed. Understanding how our politics and our behaviour is being monitored and influenced by new digital technologies such as psycho-graphics is doubly alarming because it is so difficult to understand. But Bartlett has the gift of clarity and isn't afraid to speak his mind. “That a small clique of private companies”, he says of Facebook, Twitter, Google, “have so much power over the structure and content of public debate, what information we receive and how we communicate, seems to me to be completely and utterly insane”.

That is the essence of the Cambridge Analytica story. Yes, the scraping of data and the targeting of ads may not be as effective in delivering votes as the people selling this tech to political parties claim it is. But the sheer concentration of this data is sinister. It is the cross-referencing of millions of Facebook profiles with the huge commercial databases compiled by insurance companies, credit rating agencies, even government departments - and yes newspapers because as Bartlett says, “we're all at it”. Labour and Hillary Clinton used data mining just as much as Trump and Vote Leave. Bartlett doesn't lazily assume that it's only Brexiteers who've gone over to the dark side.

Big Data gives big power because it offers those in possession of it a privileged insight into our very souls. Individual citizens are becoming an assemblage of data points which, when crunched by data scientists, reveal the most personal aspects of our nature: what we believe, our hopes and fears, our political choices, our religious inclinations, even our propensity to commit crime. Predictive policing is only a click away.

More worrying still, we are just at the beginning of this process. Once Artificial Intelligence starts acting on big data then we face the very real possibility that our lives may come to be governed by agencies, outwith our control, which know so much about us that they can predict our very behaviour and thus seek to influence it without our knowing.

This isn't just Russian trolls interfering in the US presidential elections with fake news designed to polarise opinion. Bartlett foresees a libertarian dystopia dominated by a handful of AI-rich billionaires who have largely supplanted democratic governance itself. “Democracy,” he says, “is analogue rather than digital”: it is slow, deliberative, rational. There's no guarantee it can survive in the digital cauldron of emotion and mob politics. The portents from the countries at the leading edge of tech are not good.

In China, where every single citizen will soon be tracked by facial recognition software using 570 million cameras, the Communist government is currently developing a system called Social Credit. Each of its 1.3bn citizens will get a rating based on every known aspect of their life: financial status, social engagement, criminal activity, professional achievement, consumption patterns and of course political correctness. Everyone will have a number over their head which the government says will create a “glorious trust society”. It's also a living hell.

The choice is between the Scylla of rampant inequality and social disintegration under job-killing turbo-capitalism, or the Charybdis of a digitally-powered techno-authoritarianism. Our only hope of avoiding these futures, and releasing the potential of digital technology to increase society's wealth and knowledge, is to insist on democratic oversight and full transparency, especially of the algorithms that increasingly run our lives.

At an individual level, Bartlett urges us to adopt what he calls a “principle of charity” - just stop demonising people on social media who disagree with you. That sounds like 2000-year-old Christian morality as a salve for the “toxic disinhibition” of the web. Bartlett sometimes gets carried away with his own rhetoric, but I can't think of a more important book right now. Shame those woefully ill-informed US Congressmen didn't get a copy before they interrogated Mark Zuckerberg.