As they search for reasons to be cheerful about Britain, the liberal-minded can latch on to the comforting notion that at least we do not allow the propaganda channels of American television on to our screens. We may have Jeremy Clarkson, Frankie Boyle and every other variety of media braggart and bully, but our regulators spare us a local version of Fox News.

The Broadcasting Code guarantees the fairness of television in Britain. It tells stations that they must display "due impartiality and due accuracy" and forbids them from giving "undue prominence" to their owners' favoured views. These rules are all that stand between the British and the state- or oligarch-controlled broadcasters much of the rest of humanity must endure. I cannot find polls or research to justify this hunch but I guess most people believe in broadcasting impartiality and are grateful for the benefits it brings.

For how much longer, I wonder. When I spoke to Tony Close, director of standards at Ofcom, who is meant to enforce the code, his language was suspiciously woozy and prevaricating. Instead of enunciating the clear, hard principles, which have kept broadcasting honest, he began to babble about fostering "diversity" and granting "flexibility" to foreign broadcasters transmitting in Britain.

The foreign broadcaster he had in mind was Press TV, the state network of Iran, a hostile foreign power, whose agents have just looted the British embassy in Tehran. To describe the regime's output as more propagandistic than anything the Murdoch clan produces is to understate the case in two respects.

If whites ran Press TV, one would have no difficulty in saying it was a neo-Nazi network. It welcomes British Holocaust-deniers such as Nicholas Kollerstrom, fascist ideologues such as Peter Rushton, the leader of the White Nationalist party – an organisation that disproves the notion that the only thing further to the right of the BNP is the wall – along with, until recently, Ken Livingstone, Labour's candidate for mayor of London, who showed no embarrassment about the company his Iranian paymasters kept.

Press TV is not just a home for those with exterminationist fantasies about wiping Israel off the map, but a platform for the full fascist conspiracy theory of supernatural Jewish power. Other fantasies follow. The 9/11 attacks on Washington and New York and 7/7 attacks on London were inside jobs, according to its commentators. Plots emanating from Buckingham Palace, and orchestrated by that sinister figure, the Queen, threaten its journalists.

As pertinently, the hatreds it fosters are as much directed against Iranians as the regime's enemies. Press TV shows once again that the first task for servants of a dictatorship is to control their own people. Writing on Gozaar, an invaluable website from Iran's democratic opposition, a former journalist described how eager his colleagues were to justify the suppression of Iran's 2009 uprising. A handful of anchors and photographers quit their jobs, he said, but most had no problem churning out reports that labelled protesters as terrorists.

The loyal hacks were not only Iranian mozdoor – "mercenaries" – as they are known in Tehran, but foreign journalists too. "The majority of the American-Iranian and British-Iranian staffers championed Press TV's coverage as a counterbalance to what they considered biased warping of the story by western media," the ex-reporter said. "Iranian knee-jerk conspiracy thinking was embossed in their minds."

Not much "due impartiality and due accuracy" in Press TV's reporting of the Iranian revolution then: it was all cover-up and no coverage. Nor did the network give due prominence or right of reply to those who opposed Iran's support for Syria's suppression of its revolutionaries. Jody Sabral, who by her own account was a rather naive reporter, took a job as Press TV's Istanbul correspondent. She thought it would be her "lucky break" into broadcasting. She wised up fast and appealed to liberal-leftists who make excuses for anti-western tyrannies – come on, you know who you are – to hear her out.

After months of ignoring the Syrian revolt against Iran's clients in the ruling Alawite clique, a Press TV editor allowed her to go to Turkey's border with Syria to talk to the refugees running for their lives. On no account was she to discuss their suffering, however. The real "story" was that Turkey was smuggling weapons to the Syrian revolutionaries. "When I asked what our source was, he couldn't answer, and instead he replied, 'Turkey will do anything to get into the EU.' It was a laughable response and I obviously refused to go."

She resigned and told tyrannophile westerners that the "next time you blindly back an alternative voice such as Press TV because it suits your own political view take a moment to question the quality of that information".

Ofcom won't perform that basic task. It can be shocked. The regulator announced it had been amazed to discover that Press TV (London) is controlled from Tehran – who would have thought it? – and instructed it to amend its licence accordingly. It can impose punishments. Last week, Ofcom fined it £100,000 for broadcasting an interview with the Iranian-Canadian journalist Maziar Bahari and forgetting to tell the viewers that his "confessions" had been obtained under duress in an Iranian jail. But it will not revoke its broadcasting licence.

If the clerical state bought British newspapers or set up websites, I would not call for regulators to compel them to be accurate and impartial, and ban them if they refused. I would argue against the clerics' doctrines and conspiracy theories, but accept that they had a right to put their views. They deny that same free speech to the subject population of Iran, but no matter: liberty means allowing freedom to people who have done nothing to deserve it.

Enforced impartiality in broadcasting, however, is still a cause that is worth defending from the attacks by corporations and governments which are aching for the right to propagandise and the betrayals of Ofcom officials who subvert fairness in the name of "diversity". Society is entitled to say that there should be a corner in the marketplace of ideas where journalists and their managers and owners must respect notions of fairness and balance, particularly when radio and television stations continue to be controlled by the state or by wealthy individuals and corporations.

You do not need to go to America or Iran to see what foul broadcasting follows when those principles are abandoned. Thanks to Ofcom, you can find it on your Sky box right here in Blighty.