A boy near the site of drone missile attack in Pakistan near the Afghanistan border on 19 November, 2008. Photo via EPA

British law enforcement and intelligence agencies have contributed for years to a secret NATO "kill list" of suspected terrorists and drug traffickers, according to a new report.

Evidence drawn from court and from documents leaked by Edward Snowden, which has been compiled in a 50-page report by human rights charity Reprieve, indicates that Britain has been a key partner for the US in drawing up targets for extra-judicial killings in drone and aircraft strikes in Afghanistan and Pakistan, which have killed civilians.

The claims pile pressure on the UK government to explain its role in secret kill-or-capture lists, understood to inform special operations, following revelations published by VICE News on Thursday that UK intelligence contributed to a kill list in Yemen. Former US ambassador to Yemen Stephen Seche was among a number of officials who told VICE News that British sources helped compile a "targeting list" in the region.

Now two senior British members of parliament (MPs) have called for an inquiry into Britain's role in the assassination lists.

"The suggestion a British policing agency should provide intelligence to enable the deliberate killing of drug dealers challenges principles at the heart of British law enforcement," independent MP David Davis told the Mail On Sunday. "The Government must explain precisely what it has authorised and initiate an inquiry."

"This report raises extremely serious concerns and cannot be ignored," added shadow home secretary Andy Burnham MP.

The Nato Joint Prioritized Effects List (JPEL) — a list of individuals in Afghanistan who coalition forces try to capture or kill, or just kill — was first exposed by German newspaper Der Spiegel in 2014 following a release of documents leaked by Edward Snowden, the whistleblower from the US' National Security Agency (NSA). The documents date from 2009, but it is not known how long the 669-name JPEL had been in existence.

Snowden released a copy of the JPEL, and a crucial piece of evidence in the form of a 2010 article from the National Security Agency's internal magazine, SID Today. The "top secret" classified article describes the work of FGS2F — an NSA unit in Atlanta — in supporting counter-narcotics operations, and confirms the involvement of the UK intelligence agency GCHQ and the UK's Serious Organised Crime Agency (SOCA, now the National Crime Agency (NCA)) in drawing up the kill list.

It states that the unit "and its colleagues at GCHQ has provided real-time intelligence to over 20 counter-narcotics operations, netting thousands of kilograms of drugs, detainees and weapons." One of the operations supported by FGS2F was the largest single drug seizure in history — amounting to 237 tons of hashish.

The report lists colleagues "located at GCHQ, the Joint Narcotics Analysis Centre London (JNAC), and the Interagency Operations Coordination Centre (IOCC) in Kabul."

According to the report, Intelligence from the JNAC was used to direct strikes in Afghanistan and Pakistan — which has never been a declared war zone.

The article describes a convoy led by a "primary target" named as Mullah Multan was hit by a strike as he drove from his home in Pakistan: "Though Mullah Multan survived the strike... he suffered the loss of over 3 tons of opium along with six of his cohorts."

Drug traffickers were first added to the JPEL list in 2009, "allowing them to be targeted for strikes. In October 2008, Nato defence ministers agreed narcotics trafficking networks were legitimate targets for the International Security Assistance Force (ISAF), due to the traffickers' ties to the insurgency."

The targeted killing of serious criminals — as opposed to terrorists — may not be supported by international human rights law, which only permits the use of lethal force outside of armed conflict situations if it is strictly necessary to save human life.

A 2013 British High Court legal action brought by Afghan bank executive Habib Rahman over the killing of several of his family members in a 2010 air strike brought the first claims of UK police involvement in the JPEL.

NATO forces launched a missile strike against a convoy in Takhar province, believing they were targeting an insurgent leader. But instead of hitting a man called Muhammad Amin, an alleged member of the Islamic Movement of Uzbekistan, the missile killed five men who were relatives of Rahman.

Amin was subsequently seen alive, and Rahman mounted a legal challenge which stated that information from SOCA was used to help the US military decide whom to target.

The case revealed the existence of a 2009 Senate Foreign Relations Committee report, which claimed SOCA was closely involved in the drawing up of the JPEL.

The Senate report's lead author, Douglas Frantz — then a top aide to John Kerry — said in a statement that he was a witness to briefings that left him in no doubt of SOCA's involvement.

"The statements made by the Soca officer quoted in the report and by others during my trip to Afghanistan led to my understanding that Soca was indeed involved in collecting and evaluating evidence as part of the preparation of the [list]," Frantz said.

Around 50 suspected drug traffickers were on the list in the summer of 2009, he said in a sworn affidavit.

SOCA admitted working with other agencies in Afghanistan, but denied involvement in the JPEL, saying it would only pass on intelligence that might lead to an extra-judicial killing "where the target poses a significant and immediate threat to the lives of others." The High Court's Mr Justice Irwin ruled this was "critically different from placing a person on a list for planned killing'" and the lawsuit was dismissed.

However the growing evidence casts serious doubt over British Prime Minister David Cameron's claim last September that the UK's participation in the targeted killing of Mohammed Emwazi — better known as the Islamic State executioner Jihadi John — was a "new departure" for Britain. In particular, the allegation that a UK law enforcement agency — as well as an intelligence agency — contributed to the list has provoked calls for an inquiry.

Reprieve's director Clive Stafford Smith called for an urgent review of UK policy dating back to 2001.

"For a country that loudly proclaims its opposition to the death penalty even after a fair trial, the hypocrisy is stunning: now we know that UK authorities are deeply involved in executing all kinds of people, including alleged drug dealers, without a trial at all," he said. "If democracy means anything at all, the Prime Minister must order a full and transparent inquiry into the UK Kill List, starting immediately."

Baroness Stern, co-chair of Britain's All Party Parliamentary Group on drones, praised the Reprieve and VICE News investigations.

"The Reprieve and VICE News investigations raise important questions about the involvement of the UK in targeted killing outside traditional battlespace — and knowledge and oversight of these matters in Parliament. Members will need to consider whether a new inquiry is needed, beyond the remit of the welcome JCHR inquiry into UK drone use."

The UK Foreign Office — which is responsible for GCHQ — said that it "does not comment on intelligence matters." The NCA declined to comment.