At 9pm last night, with a knock on the door of a 19-year-old man, Kent police hammered another nail into the coffin of free expression in the UK.

Earlier in the day the unnamed man from Aylesham had allegedly posted a photo of a poppy being burned, with a crudely worded (and crudely spelled) caption. He was arrested under the Malicious Communications Act and held in the cells overnight to await questioning.

It is of course just the latest in a succession of police actions against individuals deemed to have caused offence: mocking a footballer as he fights for his life on Twitter; hoping British service personnel would "die and go to hell"; wearing a T-shirt that celebrated the death of two police officers; making sick jokes on Facebook about a missing child, the list goes on. A few months ago, these could have been dismissed as isolated over-reactions or moments of madness by police and judiciary. Not any longer. It is now clear that a new criminal code has been imposed upon us without announcement or debate. It is now a crime to be offensive. We are not sleepwalking into a new totalitarianism – we have woken up to find ourselves tangled in its sheets.

News of the arrest was first announced on Kent police's Twitter feed, and it didn't take long for users to spot the painful irony of their official avatar, which simply says Kent police 101. The number is taken from the non-essential police phone number, but as we all know, Room 101 was where Winston Smith was taken in George Orwell's 1984 to be tortured and eventually persuaded to recant his individual beliefs and fall into line with officially sanctioned viewpoints.

The Orwellian allusion inevitably fed countless suggestions that we are, or are becoming, a police state, a dictatorship, even a fascist society. Such allegations miss the point: they use a 20th century microscope to analyse a 21st century problem. The Orwellian model of tyranny was invariably nailed to political propaganda, and the policing of thought-crime served only to protect and preserve a political elite or ideology. This is not what is happening in modern Britain. The new tyrant is not an oligarch or a chief of secret police, but an amorphous, self-righteous tide of populist opinion that demands conformity to a strict set of moral values. What we are seeing has less to do with the iron heel than with the pitchfork.

Last month in Lancashire, 20-year-old Matthew Woods posted some sick jokes about missing child April Jones. Almost instantly, his name and photo were being circulated with messages asking "who is this sick bastard?" Within hours, dozens of angry people had gathered outside a house that had (wrongly) been identified as his home. He was arrested elsewhere, and two days later imprisoned for 28 days. No charges were brought or investigations made into those who were circulating direct threats against Woods, publishing his supposed address or potentially inciting a riot. Where was the real crime here?

It should go without saying that throughout history, there has rarely been an opinion of value that didn't cause outrage and offence to many. This is not to say there is any ethical value or political merit in any of the cases we've seen, but that is not the point, the precedent has been set. Few seem to appreciate how arbitrary and how terribly dangerous this new tyranny of decency could quickly become.

If Woods's jokes were so offensive, why were no charges brought against the newspapers and other media that reprinted them in full, thereby exposing them to an audience of millions? If yesterday's photo of a burning poppy is so hurtful, why are the police not banging at the door of Sunny Hundal, who instantly reprinted it on Liberal Conspiracy, or any of the thousands of us who have since shared it on social media? If Barry Thew's T-shirt was so obscene, why did Sky News and countless other outlets immediately run a photo of it for everyone to ogle? If the ravings of the "racist tram lady" were so outrageous to public decency, why did millions of us send each other the link?

The truth it is not really the message, not the image, not the words that are being punished in any of these cases, but rather a refusal to conform to a tabloid-esque, lowest common denominator of decency. Our political class, media, police and judiciary all cow to this, because they themselves fear the anger of the mob. In many ways, the new tyranny has less in common with Stalin or Mussolini than with the grassroots fundamentalism, puritanism and vigilantism of the Taliban, transposed to a hi-tech, secular, networked, postmodern society. How tragic that on Remembrance Sunday, when yet another young British serviceman died fighting that very same oppression, we seem willing to surrender to the very same impulses at home.