The UK government has paid substantial compensation to Abu Zubaydah to settle claims of British complicity in his torture by the CIA.
Zubaydah has been held without trial at Guantanamo Bay since 2006 after being subjected to so-called enhanced interrogation techniques.
British intelligence agencies MI5 and MI6 admitted passing questions to the CIA despite knowing he was being severely mistreated.
The legal claim argued that UK agencies were complicit in torture, leading to a confidential financial settlement.
The compensation is important, it’s significant, but it’s insufficient.
Helen Duffy said.
She said Zubaydah’s rights violations are ongoing and urged the UK and other governments to ensure his release.
The Foreign Office declined to comment on intelligence matters linked to the case.
Former attorney general Dominic Grieve said the settlement was unusual but that what happened to Zubaydah was plainly wrong.
Zubaydah was captured in Pakistan in 2002 and held in secret CIA detention sites before being transferred to Guantanamo.
US authorities later withdrew claims that he was a senior al-Qaeda figure.
Parliamentary reports in both the UK and US criticised his treatment and the role of allied intelligence agencies.
Zubaydah remains detained without charge and is unable to access the compensation paid to him.