The first thing I learned in journalism school was not to say anything bad about the police. If I did, even if I'd seen abuses of power with my own eyes, I could face a suit for damages that would ruin me, my editors and whatever paper had been unfortunate enough to publish my work.

Nick Cohen's new treatise on censorship, You Can't Read This Book, airs one of the more painful secrets of the British press - the slide, especially over the last 15 years, towards a culture where archaic libel laws give the wealthy and privileged "the power to enforce a censorship that the naive supposed had vanished with the repressions of the old establishment."

I recently spent some time in the United States, where the cultural attitude to freedom of the press is rather different. A country that produced Fox News and allows presidential attack ads to run on television can hardly be held up as a gold standard for fair and unbiased reporting, but if American journalism lacks deference, British journalism is crippled by a surfeit of it.

Where writers in the United States are used to having their articles cross-referenced by fact-checkers for accuracy, journalists in Britain have our work picked over by lawyers. I found myself blushing when I explained to fellow writers covering police brutality at Occupy Wall Street that where I come from, it does not matter whether or not what you write is true so much as whether or not it is actionable.

Actionability, moreover, is relative. It's about money as well as legality. The decisions writers and editors make about what to publish inevitably depend on whether the potentially aggrieved party is wealthy enough to sue. This means, in practical terms, that journalists can and do say pretty much anything we like about, for example, single parents, immigrants, the unemployed, or benefit claimants. Last year, however, when a group of chronically ill and disabled benefit claimants set up a small website campaigning against Atos Origin, the private company running the controversial new welfare tests, the French company lost no time sending out intimidating legal letters.

The real problem here is not just censorship, but self-censorship. Cohen points out that British journalists, campaigners and others learn to modify our speech before it ever reaches the point of contention. I will never forget being quietly reminded by other activists, on a demonstration against corporate tax avoidance last year, to chant "tax avoider!" not "tax dodger!". The imprecision of "dodger" might have given grounds for a suit, and we'd already spent all our money on the placards.

These were young people quite prepared to be arrested in the course of a peaceful protest. The risks of a defamation action, however, were much too high. Under British civil law, the burden of proof in cases of libel or slander is on the defendant, not the claimant - if you're sued, you have to prove that what you said isn't libellous, and defendants must pay some court costs whatever the verdict. The price of losing a libel case often runs into millions, so editors, activists and journalists are forced to take steps to avoid them at any cost.

In the British media, the cost of courage is prohibitively high - so young journalists are taught to be duplicitous from day one. We are taught, or we learn on the job from decent editors shackled by the threat of libel costs, to withhold or obscure what we know in case it inconveniences the rich and spiteful.

What could be more dishonest? Without a change in the law, journalists will continue to learn deference and duplicity in the very profession many of us entered to expose such things.