I shuddered at the news that Japan has finally hanged the remaining six sarin killers of 1995, as well as their leader. It was not the ghoulishness that dismayed me, but the return to fashion of execution under the guise of counterterrorism. Capital punishment has long been a populist cause. Four years ago, a majority of Britons still supported its return, and even now public opinion is balanced.

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What odds on its revival? This week the former foreign secretary Boris Johnson justified Britain cooperating in the American trial of two formerly British jihadis captured in Syria – even though their trial could result in their execution – on the grounds that Britain itself executed such people with drones in the Middle East, including “Jihadi John”. He said: “I don’t remember hot tears being wept for him.” Such extra-judicial executions were “payback” for “credible accounts of bestial behaviour”. They are fine.

Britain abolished the death penalty in 1969. Thirty years later it signed protocol six of the European convention on human rights, which prohibited capital punishment except “in time of war or imminent threat of war”. Then in 2004 the UK acceded to protocol 13, prohibiting the death penalty “in all circumstances”. Successive governments have refused the extradition of British citizens to anywhere that puts them at risk of torture or execution. Though the citizenship of the two jihadis has been revoked, they remain covered by British policy.

The decision not to seek assurances that the death penalty will not be used in this case is a move away from this position. The Home Office minister, Ben Wallace, has explained that the two men being held in Syria were suspected of Isis-related killings, but a British court might have trouble convicting them. Johnson elaborated on this excuse. He says the decision – which he took with the home secretary, Sajid Javid – not to oppose a trial in the US was based on a balance of risks. One was indeed that they might be executed in the US, but the other was that they might be released to “roam the streets” of Britain.

Exploiting the word terrorism to extend executive discretion is now the occupational disease of power

Better to outsource their trial and possible execution than leave British streets at the mercy of the crown prosecution service. I cannot imagine a more glib reason for overturning half a century of policy on capital punishment. This is judicial rendition. The government has now been forced to temporarily suspend cooperation with the US to allow a judicial review of its decision.

A widespread litmus test of a liberal state is that it does not deliberately kill its citizens, whatever the reason. o person should be considered beyond redemption, even if in custody. But liberalism goes further. The establishment in such states claims a prerogative to override public opinion on such an issue. But Johnson clearly sees executing jihadis, even abroad, as a cherry on a populist pie.

Britain’s use of execution by drone strike has been justified by ministers on grounds of imminent threat to national security, and according to the rules of war. But a distant terrorist cannot meaningfully “threaten” a state, nor has Britain declared any war. The policy clearly defies the European convention, signed by Britain. Exploiting the word terrorism to extend executive discretion is now the occupational disease of power. Britain used to attack the former US president George W Bush for claiming a “war” to justify rendition and torture after 9/11. Yet British leaders since Tony Blair have persisted in similar language – that intervention in the Middle East is “a war to make British streets safer”.

Three years ago, an RAF operative somewhere in Lincolnshire directed a drone to kill a Cardiff man in Syria, and then his wife and his 12-year-old child. Apparently they posed “a threat to national security”, nothing more. This is the kind of language used by the Kremlin to justify its outrages. The regular use of air-guided bombs to kill people – some of them inevitably innocent – has no connection to the integrity of the British state. Such extra-judicial killings are less justified even than America’s and Japan’s, which at least follow judicial process. Drones hover over communities, raining terror and death on “guilty” and innocent alike, in flagrant defiance of the rule of law. Air strategy has not advanced since Dresden and Vietnam.

Whitehall’s use of judicial rendition shows how easily policy can be perverted when divorced from a sense of proportion, poisoned by political inexperience and ambition. If Javid, Johnson and Theresa May really feel terrorism requires tighter laws, they should put them forward for public debate, as the Home Office has been doing regularly for decades. Legislative change by executive action is pure Bush-Trump.

Returning jihadis clearly pose a challenge to the security services. Those services have been massively enhanced to meet it, and I am sure are up to the task. To equate knife attacks and hate speech with treason against the state, as did Tory MP Tom Tugendhat this week, is ludicrous. This is the language of authoritarian chauvinism. Exaggerating the “terrorist threat to Britain” has become a nationalised industry. It is undermining British justice, flouting British values, corrupting British policy and jamming central London with hideous fortifications. May once said: “We will not give in to the terrorists.” She has done just that.

• Simon Jenkins is a Guardian columnist