NEW YORK ― The ordeal of David Miranda ― the partner of Guardian columnist Glenn Greenwald detained at London’s Heathrow Airport, interrogated for nine hours, and forced to surrender his electronic devices (some of which allegedly contained documents leaked to Greenwald by the former U.S. intelligence contractor Edward Snowden) ― is a shocking demonstration of the changed climate surrounding the press.

So is the fact that state officials threatened Guardian editor Alan Rusbridger with criminal charges and forced Guardian employees to destroy computer equipment at the newspaper’s offices. But what is most shocking is that all of this happened in the United Kingdom.

As the head of the government that carried out these acts, British Prime Minister David Cameron has betrayed his country’s most noble cultural legacy. Indeed, Britain essentially invented and gave the rest of the world the idea of free speech.

As far back as the seventeenth century, whenever monarchs or parliamentarians would try to control Britain’s press, British pamphleteers and polemicists would fight back ― and often win. In the face of anti-monarchist revolutionary fervor, Parliament ― as Cameron should recall ― passed the Licensing Order of 1643, which imposed pre-publication censorship on the British press. Booksellers protested, and the following year John Milton published “Areopagitica,” a foundational statement of our modern philosophy of the right to free expression.

Returning to British first principles, the House of Commons rescinded legislation suppressing press freedom in 1776.

After that return to sanity, it was hard to convict someone for political speech or writing in Britain. No law specifically censored political speech, leaving only the much higher legal threshold of “disturbing the King’s peace.” Despite a flood of Jacobin propaganda from revolutionary France, British parliamentarians remained committed to the idea that freedom of speech and the exposure of ideas to open debate would serve Britain best.

Efforts in 1823 and 1856 to pass laws constraining free speech were shouted down by members of Parliament using very modern-sounding objections: any curtailment of press freedom constituted a “slippery slope,” while one man’s sedition or blasphemy was another man’s common-sense opinion.

British citizens, too, routinely rose up against efforts to curtail press freedom. Indeed, when the rising power of groups like the Society for the Suppression of Vice began to initiate prosecutions of publishers and booksellers, MPs attacked this behavior for its anti-British nature.

Of course, it is precisely this tradition of free speech and debate that has so often led the British press to “go too far” for the comfort of state officials and citizens alike. Parliamentarians were offended by press coverage of Queen Caroline’s divorce in 1820, and by newspapers’ mockery of King George IV.

In the 1860s and 1870s, they were appalled at how publishers boosted newspaper circulation by reporting on divorce courts (and the scandalous behavior of individual politicians). Political elites called again and again for curtailment of press freedom. But Parliament and courts always returned over time to the core British value of free speech and expression.

Will today’s constrictions on journalism in the U.K. be similarly transient? In the wake of the hacking scandal at Rupert Murdoch’s News Corp, Parliament pressured the British press into agreeing to a terrifying system of fines of up to a 1 million pounds ($1.6 million) for news “errors.” The same system (recently put in place in Australia as well) has often been used by less democratically inclined governments to suppress independent, vigorous journalism; in Ecuador, for example, newspapers are regularly fined large sums for criticizing the government.

The establishment of “national security” and “fighting terrorism” as stalking horses for intimidation of journalists who are doing their jobs ― exposing government abuses to the light of day ― gives the state an even more effective tool to suppress investigative reporting. Dictators everywhere silence journalists in the name of “national security” by charging those who would investigate their regimes with treason, subversion, or espionage.

The same tactic is now appearing in democracies, too ― with the same chilling effect. Indeed, perhaps the most dismaying aspect of the Snowden story has been the relative silence of other news outlets, in Britain and America, as the national-security state literally comes to the Guardian’s door. Instead, we have Michael Grunwald, a senior correspondent at Time magazine, posting on Twitter (and then deleting): “I can’t wait to write a defense of the drone strike that takes out Julian Assange.”

As the nineteenth-century German poet Heinrich Heine presciently observed, where they burn books ― or smash computer hard drives, one might add ― soon they will burn people.

Do other British publishers really believe that silence will protect them from the slippery slope? If the Guardian must stand alone now, next it will be the Daily Telegraph or the Financial Times that will face menacing calls from Whitehall and demands to spike a story or hand over the documents involved in an investigative report.

Britain needs to reestablish the primacy of free speech. It needs to dismantle the new system of fines that is being developed (a system that, paradoxically, the Guardian’s Rusbridger and the Labour Party ― but not Cameron ― have eagerly supported), exempt journalists from detention under the Terrorism Act, and forbid prior restraint of publication.

Unfortunately, there is little movement in this direction. Some MPs signed a letter to Cameron from the Committee to Protect Journalists protesting Miranda’s detention. But much more needs to be done. Above all, Cameron’s political future ― and that of all U.K. politicians ― should depend on whether he upholds Britain’s tradition of free speech and public debate or continues to betray it.

For their own sake ― and for that of Britain ― other U.K. media organizations should stop flirting with censorship and lead this campaign.

By Naomi Wolf

Naomi Wolf is a political activist and social critic whose most recent book is “Vagina: A New Biography.” ― Ed.

(Project Syndicate)