Binyam Mohamed came to the UK as an asylum seeker in 1994
UK security agencies were "mixed up in wrongdoing" related to the torture of a British resident now held by the US in Guantanamo Bay, a court has been told.
Binyam Mohamed's lawyer said the UK had received reports that were the "fruits of his interrogation".
Mr Mohamed wants the High Court to force the government to release evidence he says will support his claim he gave testimony after torture.
The 30-year-old, of west London, has been charged with war crimes in the US.
Mr Mohamed is the last recognised British resident held at the US detention camp in Cuba.
He could face a military tribunal and get the death penalty if convicted of conspiring to commit terrorism.
He denies involvement in terrorism.
Dinah Rose QC told the High Court that Mr Mohamed could get the charges dismissed on the basis that evidence was obtained by torture and was inadmissible.
She said there were strong grounds for believing that the Secret Intelligence Service (MI6) and Security Service (MI5) had independent evidence supporting the claims of torture.
"The defendants [the Foreign Office] are under an obligation to disclose documents because the British authorities were mixed up in wrongdoing in this case," said Ms Rose.
"The British assisted the Americans, and the US authorities provided the UK with the fruits of his interrogation."
Ms Rose claimed that at a time when the UK had sufficient information to suggest Mr Mohamed was probably being tortured, "it provided to the US authorities detailed information, and lists of questions to be put to Mr Mohamed in his interrogation".
'No legal obligation'
Foreign Office lawyers say the department has acted within its powers and is not legally obliged to disclose the evidence sought.
The department says it has released some information about the case, but that other disclosures could seriously damage national security.
The lawyers also argue that the US legal system will safeguard Mr Mohamed's rights.
The US charge sheet alleges Mr Mohamed travelled to Afghanistan in May 2001 and trained at an al-Qaeda camp.
It says he then accepted instructions from al-Qaeda leader Khalid Sheikh Mohammed to conduct terror operations in the US.
Mr Mohamed was detained in April 2002 as he tried to return to the UK from Pakistan.
He says he was tortured in Pakistan, and again after being transferred to Morocco then Afghanistan.
Mr Mohamed claims that torture over a period of 18 months in Morocco included having his genitals repeatedly slashed with a razor blade.
Foreign Secretary David Miliband formally wrote to his US counterpart Condoleezza Rice in August 2007, asking for Mr Mohamed's release.
Mr Mohamed, who was born in Ethiopia, came to Britain as an asylum seeker in 1994, aged 16.
His asylum claim was never finally determined but he was given leave to remain and went on to work as a cleaner in west London.
The two-day hearing continues on Tuesday.