Targeted assassinations via drone strikes, such as the killing of Iran’s Qassem Suleimani, have become progressively normalised with the help of official secrecy, government propaganda and some uncritical press coverage, according to a report.

In The Frame, published by pressure group Drone Wars, concludes that “an easy narrative for targeted killing” had been constructed by the UK and the US during the conflict with Islamic State, where several high-profile individuals were killed by drones and the existence of a British “kill list” emerged.

Chris Cole, the director of Drone Wars, said it helped reinforce the justifications for the US assassination of Suleimani, the leader of the Quds Force in Iran’s Revolutionary Guards, earlier this month.

“It is surely unarguable now that drones have enabled and normalised a culture of targeted killing which is eroding international law norms and making the world a more dangerous place,” Cole said. He argued the recent strike could usher in a violent “new era in drone warfare”.

The study, conducted before Suleimani was killed, examines drone strikes carried out between 2015 and 2018, including the lethal targeting of Briton Reyaad Khan by the RAF in September 2015, as well US strikes on Mohammed Emwazi the same year and two years later on Sally Jones.

It concludes that then prime minister David Cameron and other ministers under his premiership and since have focused on the “the notoriety of individual British Isis members” to justify their actions, whilst relying on military secrecy to avoid a wider policy debate.

The report’s author, Joanna Frew, says there was considerable coverage of the first acknowledged killings of Khan and to a lesser extent Emwazi in 2015, but that dropped off as the conflict continued, with less reporting of the killing of Jones despite her media notoriety as the “white widow”.

Looking at the BBC, the Times, the Daily Mail and the Guardian, Frew said that there were 127 news articles that discussed Khan’s death in more than one sentence, 67 for Emwazi – dubbed by the tabloids as “Jihadi John” – and just 26 for Jones, who was killed in October 2017, possibly with her 12-year-old son Jojo Dixon.

An acknowledgement in the Daily Mail in February 2017 that British RAF pilots were “working their way through” the kill list was only cited in a handful of other media articles. The killing of Naweed Hussain by a US drone strike, guided by intelligence from the RAF, was only made public in 2018, a year after it had happened.

Coverage of the drone strikes was largely conducted impartially according to Frew, but there were a significant minority of pieces in the Daily Mail (48 in total) and the Times (35) that were judged to have “expressed support”.

The report’s author looked at 329 articles in total. A much smaller number – 26 overall – were critical, with 16 in the Guardian, five in the Mail and four in the Times. All but one of the BBC articles were impartial, Frew added.

Ministers also switched away from relying on legal justifications, as Cameron had in the case of Khan, who had been accused of plotting imminent terror attacks on the UK, so justifying the attack on the well established grounds of self-defence. When Emwazi was killed the prime minister also said it was “the right thing to do”.

Given Emwazi’s involvement in the notorious Isis “Beatles” cell which conducted filmed executions of hostages, Frew said the argument was not surprising and effective. But she added it also has the effect of placing the target “as beyond redemption, beyond the rule of law, where a legal justification is not necessary”.

International law around targeted killings is complex, but in theory they are only legitimate as acts of self-defence by a state, where the threat is imminent, meaning overwhelming and immediate. But the doctrine of imminence has been eroded over recent years, the report notes.

In the case of Suleimani, an official in Iran’s government, the US said it had intelligence he was plotting further terror attacks against its citizens in the Middle East, but has not publicly released the information, which has been described as “razor thin” by sources who had seen it.

Donald Trump has said that legal justifications about the death of Suleimani “doesn’t really matter” because the Iranian commander was “the terrorist” and had a “horrible past”.

Frew, in her report, called on the UK to disclose its policy on drone targeted killing, to respond to questions about the “kill list” and engage in international efforts to develop a code of conduct about the use of armed drones. She added: “Senior ministers have played to the gallery on drone targeted killing without responding and engaging in proper debate on the legal and ethical issues.”