Thank God for polemicists, though atheist Nick Cohen won't like that sentiment.

You Can't Read This Book is a blistering onslaught on the conventional view that we're living in an age where the internet, citizen journalism and the light-speed growth of Google, Facebook and YouTube have led to unprecedented freedom of speech, information and opinion.

Cohen blames and shames "white western liberal opinion" for whom the cheerleaders are, in his phrase, "fercockt Western putzes". His first punch bag is self-censorship, an activity so widespread and instinctive that it is flourishing unnoticed in the subconsciousness and writing of western liberals.

Cohen homes in on the fatwa proclaimed in February 1989 by Iranian leader Ayatollah Khomeini, calling for the execution of novelist Salman Rushdie following the publication of The Satanic Verses. The book was condemned by fundamentalist Muslims as a blasphemous attack on Islam, and Rushdie went into hiding. He re-emerged 10 years later when the Iranian government hinted they no longer wanted to slaughter him.

Islam's critics responded to the murders of people associated with The Satanic Verses by toning down their writings about Islam. Many simply refused to write about it at all. That, says Cohen, is a glaring example of self-censorship, and compelling evidence that public sharing of information and opinion is anything but free.

Prosecution and persecution for blasphemy is not, however, reserved to Islam. In 1977 the then self-appointed guardian of Britain's morals, Mary Whitehouse, brought a private prosecution for blasphemy against Gay News and its editor, Denis Lemon, for publishing a poem, The Love That Dare Not Speak Its Name, which depicted Christ as gay. Lemon was sentenced to nine months. At least he wasn't burned at the stake. And it continues. In this US presidential election year, the US Christian right are dominating the Republican primaries. The nomination candidates are vying for support on platforms which deny evolution.

Money is Cohen's next enemy. If you've got enough of it, you can prevent media organisations publishing anything remotely damaging about you. Robert Maxwell was a master of the art. Despite a 1970 government report which said "he is not in our opinion a person who can be relied upon to exercise proper stewardship of a publicly quoted company", Maxwell later purchased the Daily Mirror which he tried to run as a private publicity machine promoting his own interests and agenda. It was only after his mysterious death in 1991 that the truth about Maxwell surfaced, including the discovery that he had stolen £440m from the newspaper's pension fund in a failed attempt to prop up his ailing business empire.

While he was alive, a threat of a libel action was enough to persuade most editors to back off from attacking him in print, not least because the costs alone of a libel action in England and Wales can exceed £1 million and are around 140 times greater than the European average. You need deep pockets and an iron will to risk that kind of money.

The sheer expense of defending a libel action in England has led to "libel tourism". The (extremely wealthy) offended parties, regardless of where they live, can almost always find a way to bring a case in England, and in theory could rely on a libellous web page published on a server hosted anywhere in the world. Neither party needs to have a connection with England to bring a case under English law.

Cohen's final target is the state, which he argues has lost much of its censorial clout as the power of the internet has grown. In pre-internet days, foreign office civil servant Sarah Tisdall, who leaked details of the arrival of US Cruise missiles to The Guardian, was jailed in 1983. After a failed legal battle by the newspaper to protect its source, Tisdall was sentenced to six months for a breach of the Official Secrets Act. To be fair, The Guardian itself did not know the identity of the source, and it took the British state to find Tisdall after officials got their hands on the document she had leaked. It was not the paper's finest hour, and then editor, Peter Preston, conceded as much in an article published in 2005.

More recently, following the introduction of freedom of information legislation in the UK, the ability of the state to limit what the public can discover has been curtailed. Without the new law, the Telegraph would almost certainly not have been able to drip-feed stories of MPs' expenses. We now know how much it costs to have wisteria removed from a chimney, the price of an artificial island to house one's ducks and the appalling expense of moat-cleaning. More seriously, several MPs went to prison as a result of the revelations, and elected representatives are now a lot more careful over their expenses claims.

Cohen winds up by challenging western liberals (not fercockt putzes this time) to continue to press for more and greater freedom; to campaign for the freedom we already enjoy to be extended to repressive regimes, and to resist demands and threats from all and any religious groups for special treatment. His title, You Can't Read This Book, is evocative of Abbie Hoffman's Steal This Book, published 40 years ago. Please, don't steal Cohen's book. Buy it or borrow it from the library.

You Can't Read This Book: Censorship In An Age Of Freedom

Nick Cohen, Fourth Estate, £12.99