The best way to imagine the British establishment is to picture a committee that never meets. There is no chain of command, which might leave incriminating paper trails; no controlling intelligence. Its members do not need to wait for instructions from on high. They know what to do without needing to be told.

Thanks to Lord Justice Leveson, policing in Britain has been sewn up. The learned judge responded to alleged crimes by the employees of Rupert Murdoch not by holding individuals to account, but by recommending collective punishment and a general assault on liberty. Police officers who knew of misconduct should not go public but seek out "confidential avenues in which they have faith", he ruled. I am sure that if there were ever an inquiry into the Leveson inquiry it would find that no one ordered him to recommend suppression. He would have known what to say anyway.

The result has been a collapse in public scrutiny of the police. Junior officers watch their senior officers being arrested for having contact with journalists, even when there is no question of money changing hands, and are "spooked", said Martin Brunt, Sky's crime correspondent. The authorities have turned the doctrine of the reforming Metropolitan police commission Sir Robert Mark on its head, wrote Duncan Campbell, who was covering the crime beat for the Guardian before most of us were born. Mark, he reminds us, told the police to "withhold only what you must". Now we are back in the old Britain where police policy is: "Tell them only what you must."

On the face of it, suppression has its attractions. Forget about the other British forces; on its own, the Metropolitan police spends £9.6m a year on a press office that has nothing worth saying to the press. The taxpayers could have that money back for a start. Meanwhile, journalists – and remember that in the age of the web everyone online is a potential journalist – might concentrate on police abuses of power if they cannot get chummy with serving officers in the News of the World style.

A look at the Andrew Mitchell scandal dispels trite illusions. Robert Harris, a friend of Mitchell's, compares it to the Dreyfus affair, the subject of his latest fine novel. Harris is going over the top, but you can see his point. France in the 1890s had a large rightwing constituency, which wanted to believe that a spy in the French army had to be a treacherous Jew. The British left in the 2010s, and many others besides, want to believe in Tory posh boys, who will abuse the brave and honest coppers willing to put themselves in the line of fire.

The accusation that members of the Police Federation concocted against Mitchell fitted modern prejudices perfectly. If they had just said that Mitchell had called the officers who tried to stop him cycling out of Downing Street "fucking morons", and left it there, it would not have hurt as much. Their masterly addition that Mitchell called them "plebs" too was the killer calumny. Deliberately or not, and the Independent Police Complaints Commissioner, Deborah Glass, says the campaign against Mitchell was a conspiracy in all but name , "plebs" carried a lethal suggestion of the patrician superiority a privileged, classical education brings. Everyone believed it, including me, to my shame.

"The beast with many heads butts me away," said Shakespeare's Coriolanus when the plebs drive him from Rome. Mitchell must have felt the same as the Police Federation, rival politicians, screaming audiences on discussion shows and a hostile media battered him out of office.

Ed Miliband, who would apologise to Mitchell if he were an honourable man, ran a propaganda campaign under the headline: "Who do you trust – the police or Andrew Mitchell?" He castigated Cameron for choosing to "believe the word of a Tory MP over the word of a hard-working police officer".

The malice of the Police Federation is equally evident. It wanted to punish the coalition for cutting spending and any target would do. Mitchell was the chief whip and had no responsibility for law and order. But he was a member of the government and that was enough, in Deborah Glass's words, to turn "a largely inaudible altercation lasting less than a minute into a national scandal that not only caused injustice to Mr Mitchell [but] brought shame upon the police".

As with Dreyfus, the "affair" goes on forever. In December 2012, Michael Crick of Channel 4 showed CCTV footage from Downing Street that contradicted the police account. Last week, the courts jailed PC Keith Wallis for a series of extravagant lies about what happened in Downing Street. Mitchell himself had taken the precaution of secretly taping a conversation with Police Federation representatives Inspector Ken MacKaill of West Mercia Police, Detective Sergeant Stuart Hinton of Warwickshire Police and Sergeant Chris Jones of West Midlands.

The officers came out of the private meeting and damned him. Even with the evidence of the tape, they would only admit to "poor judgment". Mitchell is still out of office. The chief constables of West Mercia, Warwickshire and the West Midlands still refuse to discipline MacKaill, Hinton and Jones. The Police Federation is still going to court to stop the Independent Police Complaints Commission stepping in and investigating the officers in the chief constables' place. The federation still keeps the men on as its official representatives.

I hope I do not have to deal with "whataboutery". I hope readers do not believe that the police's treatment of Mitchell does not matter because he is a Tory rather than a street kid. Justice is indivisible. You may not think much of Mitchell but he is a constitutionally elected politician – a poor thing but our own. You cannot call for justice for the victims of police lies about the Hillsborough disaster while denying justice to a victim of a political conspiracy by the coercive arm of the state.

Throughout the scandal, the police have had no difficulty leaking fraudulent accusations to the media. By contrast, Mitchell's friends have a police whistleblower who, they say, can reveal how the stitch-up was organised. But he won't go public because he is afraid of the consequences for his career. Double standards are everywhere in the post-Leveson world and anyone who expected a better outcome was a fool.

Sweeping bans and collective punishments intimidate those who can challenge established interests. Hierarchies can continue to spin and manipulate, but the few, brave people who might speak out stay silent.