One of the comforting myths of our times is that we have seen a massive expansion of freedom of expression. Perhaps a price has been paid in the explosion of inequalities between and within nations and in religious wars harking back to the 17th century. But, what the heck, these are regrettable side-effects of a much freer, better informed world.

Twitter and Facebook, together with fearless journalists and human rights lawyers, have massively expanded the boundaries of freedom, so the argument runs. Look at Iran, Egypt, Libya or China. Surely social media and the inventors of Google and Wikipedia have dumped the censor in the dustbin of history.

Nothing could be further from the truth, argues Nick Cohen in the latest of his counterblasts to conventional wisdom. Cohen is the most stimulating – if at times infuriating – columnist in our national press, largely because you never quite know where he is going to end up. He lashes the stupid left as much as the smug right. He ferrets about in the lower reaches of politics to find disturbing symptoms of what should not be happening. He has a sense of history and literature, in contrast to the dominant political generation of PPE graduates who have read every page of the Economist since they were at Oxford, but have never opened a novel.

In this vigorous polemic (which everyone involved with the Leveson inquiry should read), Cohen exposes the new censorship. At University College London, a speaker declared that Jews "have monopolised everything: the Holocaust, God, money, interest, usuary, the world economy, the media, political institutions". When some protest was made against this inflammatory 1930s-style antisemitism, the university's response was to seek to silence the protesters, accusing them of "Islamophobia".

Or take Roman Polanski, who drugged and sodomised a 13-year-old girl and fled the US rather than face justice. When Vanity Fair published a report about Polanski's behaviour, the film director sued the magazine in a London court. Vanity Fair is written and published in New York but Polanski preferred London – "a town called sue", as it is known in the global libel trade. London is where Russian oligarchs, Middle East arms salesmen and, above all, the very upstanding members of the new rich in Britain exercise the new censorship courtesy of our courts.

This is not just a narrow book on the sort of issues being dealt with by Leveson. Cohen also excoriates the liberal intelligentsia for their mealy-mouthed failure to support Salman Rushdie when Islamists started burning his books. To the shame of British freedom, John le Carré and Roy Hattersley found excuses for the mullahs. And can it be true that Ian Buruma, a writer I admire, called Ayaan Hirsi Ali an "Enlightenment fundamentalist" because she repudiated the censorship of the Muslim Brotherhood and its Islamist epigones? Surely there is no greater badge of honour than to stand with the giants of the 18th century, who insisted rationality should be given equal status to superstition.

In the name of 21st-century faith, gay people are murdered, women are stoned, girls made ill as religious garb denies sunshine to their face and bodies and doctors killed in "civilised" America if they help women control their fertility. After "Islamophobia" was invented as a concept two decades ago, the Vatican launched a campaign for the UN to recognise "Christianophobia". The right of men (always men) dressed in long robes to censor words and thought is increasing, not diminishing.

In the end, Cohen rightly argues, we have to assert the Enlightenment values of both Voltaire and Mill as they argued for free speech. That is not to be confused with freedom of information, a process that, in the US, has been hijacked by corporate interests to prevent any public discussion that might challenge their power. In Britain, we have the wondrous example of the information commissioner refusing to tell the victims of illegal media intrusion that they have been targeted. Christopher Graham, a former BBC bureaucrat, holds 4,000 names of those targeted by the media. He has sent these names to the media owners and the police, but not the victims themselves. Only in Britain would the man appointed to uphold the Freedom of Information Act as a censor.

The new authoritarianism combines religious supremacists, Chinese communists, Russian kleptocrats, "Davos men" and the Fortune 500 super-rich in a new network of postmodern censorship. We have more information than ever, but truth is harder to find and easy to suppress. Increased freedom and increased censorship co-exist. This wasn't meant to happen. Cohen asks worrying questions that offshore proprietors and their editors do not want raised and lawmakers have no easy answer to.

Denis MacShane is MP for Rotherham