A Guantánamo Bay prisoner tortured by the CIA has accused British intelligence agencies of complicity in his mistreatment in a new case before one of UK’s most secretive courts. Abd al-Rahim al-Nashiri, who is alleged by the US to have plotted al-Qaida’s bombing of an American naval ship, is seeking to persuade the court to consider his complaint against MI5, MI6 and GCHQ. Lawyers for al-Nashiri, 58, argued this week there was an “unavoidable inference” that the intelligence agencies were complicit in his torture, rendition and mistreatment by the CIA. Al-Nashiri, a Saudi Arabian citizen, was first detained in 2002 as part of the CIA’s post-9/11 secret detention and interrogation programme. He is currently facing the death penalty before a US military commission over his alleged role in the 2000 bombing. The UK government is arguing that the investigatory powers tribunal (IPT) – a special judicial body that investigates complaints against the intelligence services – does not have jurisdiction to hear al-Nashiri’s application. In papers submitted to the tribunal, al-Nashiri’s barrister, Hugh Southey KC, said: “The complainant’s case is that the UK agencies aided, abetted, encouraged, facilitated and/or conspired with the US authorities in his mistreatment.” After his capture by the CIA, al-Nashiri was put into a network of secret prisons operated by the agency, known as black sites, in Afghanistan, Thailand and multiple eastern European countries. A US Senate investigation into the CIA’s post-9/11 detention programme found that al-Nashiri was repeatedly tortured while held at the black sites. The so-called “enhanced interrogation techniques” used against him included waterboarding, mock executions and “rectal feeding”. After being held for almost four years at secret CIA facilities, al-Nashiri was transferred in 2006 to the US military prison at Guantánamo Bay in Cuba. He has been detained there ever since. In al-Nashiri’s complaint to the IPT, his lawyers said he was of “specific interest” to British intelligence in the 2000s and probably part of a group of detainees in whose torture the UK was allegedly complicit. The lawyers allege the UK’s involvement in al-Nashiri’s mistreatment probably included allowing Luton airport to be used to refuel a private jet used in his rendition from Thailand to Poland in December 2002. If al-Nashiri’s case is allowed to proceed at the IPT, it could place the spotlight back on longstanding questions about the UK’s alleged complicity in the CIA’s detention programme. In 2018, the parliamentary intelligence and security committee concluded that the UK’s spy agencies were involved in the kidnapping and torture of terrorism suspects by the CIA and other partner intelligence services. However, the committee said its investigation had been “terminated prematurely” because of government obstruction and warned: “There are questions and incidents which therefore remain unanswered and uninvestigated”. UK ministers previously pledged to hold an independent judge-led inquiry into the issue, but the commitment was abandoned in 2019. At Guantánamo Bay, al-Nashiri is awaiting trial before a military tribunal in connection with the bombing of the USS Cole that killed 17 American sailors. US officials have accused him of being “one of al-Qaida’s most skilled, capable, and prolific operational coordinators”. Al-Nashiri’s case has been closely scrutinised by the European court of human rights, which found that Poland, Romania and Lithuania committed human rights violations while helping the CIA operate black sites. The European court ruled the CIA’s secret programme was specifically designed to strip the detainees of protections in US and international law against torture, enforced disappearance and arbitrary detention. Asked about al-Nashiri’s case at the IPT, a government spokesperson said: “It is a longstanding principle that the government does not confirm or deny allegations, assertions or speculation about the activities of UK intelligence agencies.”