Always remember mornings like these, the next time police officers and politicians demand more powers to protect us from terrorism. They always sound so reasonable and so concerned for our welfare when they do. For who wants to be blown apart?

But the state said its new powers to intercept communications would be used against terrorists. They ended up using them against fly tippers. Now the police are using the Terrorism Act against the partner of a journalist who is publishing stories the British and American governments would rather keep quiet.

The detention of David Miranda at Heathrow is a clarifying moment that reveals how far Britain has changed for the worse. Nearly everyone suspects the Met held Miranda on trumped up charges because the police, at the behest of the Americans, wanted to intimidate Miranda’s partner Glenn Greenwald, the conduit of Edward Snowden’s revelations, and find out whether more embarrassing information is on Greenwald’s laptop.

The Brazilian government has gone wild. (Greenwald lives in Brazil and his partner is Brazilian.) All kinds of people are saying, quite properly, that although they disagree with Greenwald’s politics they defend the right of citizens to hold governments to account.

You might have thought the Met would have been anxious to reply to its critics. You might have thought – expected indeed – that it would angrily rebut the charges, and provide irrefutable evidence that its officers are not like the goons of a dictatorship but remain the conscientious public servants of a democracy.

The Terrorism Act of 2000, which the Met used against Miranda, says that terrorism involves ‘serious violence against a person’ or ‘serious damage to property’. The police can also detain the alleged terrorist because he or she ‘endangers a person’s life’, ‘poses a serious risk to the health and safety of the public’ or threatens to interfere with ‘an electronic system’.

I wanted to ask the Met: Which of these above offences did your officers suspect that Miranda might have been about to commit? What reasonable grounds did they have for thinking he could endanger lives or property? And, more to the point, which terrorist movement did you believe Miranda was associated with: al-Qaeda, Hezbollah, Hamas, Continuity IRA, ETA, Shiv Sena, the provisional wing of the Unabomber Appreciation Society?

Greenwald may not thank me for saying this but in one respect America is an admirable country. In the US, the police reply to reporters’ questions. They may lie, but at least they reply. In the UK, they say nothing. Chief constables could save precious money and protect front line services by sacking every police press officer in the UK. They are useless. Actually, they are worse than useless: they are sinister. They provide the illusion of accountability while blocking it at every stage.

I phoned the Met press office. You will need to read our statement before we can answer your questions, a spokeswoman said. She emailed me the statement. True to form, it said nothing worth noting:

‘At 08:05 on Sunday 18 August 2013 a 28 year old man was detained at Heathrow Airport under Schedule 7 of the Terrorism Act 2000.
He was not arrested.
He was subsequently released at 17:00.’

That was it. As I, like every other journalist on the story, had further questions, I phoned back.

‘We’re not saying anything else,’ a new flak-catcher said.

I pointed out that the Miranda detention was now an international incident, and that the Met looked as if it was turning into a political police force.

The flak-catcher bridled. ‘We are not politicised,’ he insisted. ‘We are operationally independent.’

‘You can’t just say that,’ I replied. ‘You have to prove it. You have to show you are accountable.’

‘Ah,’ said the flak-catcher. ‘We are legally accountable. But we are not accountable to the media.’

As I understand him, unless Miranda sues, the Met believes it can do what it wants, and behave as badly as it likes, without a word of elucidation or justification.

The Miranda affair is proof, if further proof is needed, that we are now stuck in the post-Leveson world where not only journalists but their partners can be detained and questioned for hours on end. Where police officers feel no need to explain themselves to the public, in whose name they work, and whose taxes pay their salaries. The next time they try to tell you that the secrecy and attempts to silence legitimate debate are ‘in the public interest’, do not forget what they did to David Miranda, because they can do it to you too.

Tags: David Miranda, Edward Snowden, Freedom of speech, Glenn Greenwald, Intelligence services, Police, Terrorism