The UK government could be the subject of legal action to uncover the truth of an air strike that it says killed a civilian in Syria in 2018.
The incident is the only time Britain has admitted responsibility for a civilian death during its operations against ISIS in Iraq and Syria.
However, it is clouded in mystery because findings by the US-led coalition against ISIS suggest there were no civilian casualties that day.
Campaigners have asked the UK’s Ministry of Defence (MoD) to release documents linked to the attack on March 26, 2018.
Joe Dyke of non-profit group Airwars told The National that activists were seeking “all documents assessing civilian harm in the incident”.
This would typically include prior risk assessments of whether civilians were likely to be harmed, he said.
The details sought by Airwars also include the exact time and location of the strike.
Defence officials have denied the release of the documents after a freedom of information request two years ago. The Information Commissioner's Office has upheld the MoD's position.
Activists now plan to take the ministry to a tribunal, which could hear the case later this year.
“These are vital questions both for the British public and for the civilians in Iraq and Syria who have been affected by British actions," Airwars director Emily Tripp said.
Erin Alcock, a lawyer representing the group, said there was a “fundamental lack of transparency” in how the UK had assessed harm to civilians.
A Ministry of Defence spokesman said: "As there has been a challenge to the Information Commissioner’s decision, it would be inappropriate for us to comment ahead of the upcoming tribunal."
The air strike came to light in May 2018 after the BBC reported claims of possible civilian deaths.
Defence secretary at the time Gavin Williamson told the House of Commons that “during a strike to engage three Daesh [ISIS] fighters, a civilian motorbike crossed into the strike area at the last moment”.
He said it was “deeply regrettable” that the motorcyclist had died in the strike in eastern Syria.
But in September 2018, the US-led Operation Inherent Resolve issued a report apparently contradicting the UK’s account.
It said that “after a review of available information it was assessed that no coalition strikes were conducted in the geographical area that correspond to the report of civilian casualties” on March 26.
The UK government has stood by its story.
A month-by-month list of British air strikes against ISIS says a Reaper drone “destroyed a terrorist vehicle in eastern Syria” on that date.
Armed Forces Minister James Heappey in 2021 said it remained the only civilian casualty known to the British government during those operations.
He said it was possible there were other cases of civilian casualties of which defence chiefs were unaware.
Campaigners have alleged British involvement in US air strikes that may have caused deaths.
An investigation by The Guardian recently cast doubt on Britain's suggestion that it caused no civilian casualties in Iraq.
Britain continues to carry out armed reconnaissance patrols against ISIS.
In the most recent known strike in December, two Hellfire missiles were fired at a building said to be housing an ISIS terrorist in northern Syria.
The coalition last year said at least 1,437 civilians had been “unintentionally killed” in strikes since 2014.
At least 35,000 strikes have been carried out during the campaign against ISIS.
