Rangzieb Ahmed, a British man of Pakistani origin and allegedly al-Qaeda's top agent in the UK, is appealling a conviction against "terrorism" offences handed down two years ago.
At the centre of the appeal, which began in London on Tuesday, are his claims that the British government was involved in the torture that he was subjected to by Pakistan's Intelligence Services [ISI] .
In 2006 Ahmed was held in Pakistan by the ISI during a British counter-terrorism operation, following which he was deported and tried in Manchester in 2008.
He was convicted of being an al-Qaeda member and also of directing a terrorist organisation.
Ahmed also admitted to membership of Harkat-ul-Mujahideen, a group considered a terrorist organisation by the British.
The 34-year-old is currently serving a life sentence in prison.
'Travesty of justice'
Judges at the court of appeal in London have heard Ahmed's account of torture carried out by the ISI, who removed three of his fingernails during questioning, and claims that Britain MI5 and Greater Manchester Police knew about it.
Ahmed, who is pushing to have his conviction overturned, says it was evidence gained during this time that was used to convict him of leading an al-Qaeda cell in 2008.
His appeal, which he has been watching via videophone from his prison cell in northern England, is expected to continue in the coming days and judges will also hear from government lawyers.
Ahmed previously sent a letter to Al Jazeera in which he calls these proceedings a "charade" and a "travesty of justice".
The UK government's response to the allegations of complicity in his torture was heard while the court was sitting in camera.
Al Jazeera's Paul Brennan said "the whole issue of complicity in torture is a very sensitive one for the British government".
"The ruling that was made by the judge [in the interim] after legal argument had finished, but before the trial which ended in his conviction, has stayed secret ever since ."
Despite attempts by the British media to have the file opened it has remained confidential.
"The suspicion is that there is something in that file which certainly MI5 and the police do not want opened, potentially embarrassing, but at the moment we simply do not know what it is," Brennan said.
"On the basis of the evidence, he [Ahmed] is a very dangerous individual, nevertheless, what the authorities do to combat such individuals is what is under the spotlight."
Source: Al Jazeera