Former defence secretary Geoff Hoon said he was shocked to discover UK soldiers had hooded and allegedly beaten to death a detainee in Iraq.
He told an inquiry into the death of Baha Mousa in September 2003, he was unaware some troops had believed hooding to be "standard practice".
He said questions needed to be raised about Mr Mousa's death in British custody.
The inquiry is investigating claims UK troops were involved in the death.
The inquiry has already heard that Mr Mousa had been hooded for almost 24 hours and systematically beaten in September 2003.
The 26-year-old hotel receptionist was found dead with 93 injuries after being held in the custody of 1st Battalion the Queen's Lancashire Regiment (1QLR) in Basra, southern Iraq.
Mr Hoon said the question that needed to be asked included: "Why was this man hooded for so long? What were the circumstances? Why was hooding being used? Was it being used for purposes that were for example unlawful?"
Gerard Elias QC, counsel to the inquiry, played video footage to the inquiry which showed six hooded and handcuffed men - one who he identified as Mr Mousa - being held in small room and verbally abused by a British soldier.
Mr Elias said the video had been taken at a temporary detention facility a day before Mr Mousa died.
Mr Hoon said it was the first time he had seen the images and added: "If it is what it appears to be, it looks pretty appalling.
"If British soldiers engaged in that, it's reprehensible."
He said: "I was clearly deeply shocked that a man had died in such circumstances at the hands of apparently British soldiers."
Earlier a senior army officer revealed he had banned the hooding of Iraqi prisoners five months before Mr Mousa's death and had also been unaware his troops still performed the practice.
Maj Gen Robin Brims, who has since been promoted to Lt Gen, said he outlawed the practice among the 1st Armoured Division in April 2003.
He gave an oral order to ban hooding in April 2003 after he saw a detainee wearing a sandbag hood at a prisoner-of-war handling centre near Umm Qasr.
He told the inquiry he was unaware the order had not been passed down.
Gerard Elias QC, counsel for the inquiry, asked him: "Did you know at the time of issuing that order that there were troops on the ground that believed it was a standard operating procedure to hood prisoners at the point of capture?"
Lt Gen Brims said: "I didn't know at the time, I now know it, yes."
He also told the inquiry that although he had not seen any evidence of a standard operational procedure telling soldiers to hood their prisoners at the point of capture, there had been some confusion about the legality of the action.
He said he had not realised he needed to make the order in writing, saying: "At the time I didn't know that was the practice and therefore, at the time, it didn't seem to me that I needed to make an emphasis on this order."
But he said he would have expected people to ensure his order was obeyed, and to take action if it was not.
Discussing Mr Mousa's death, he said he was appalled that anybody could die while in the custody of soldiers, and had urged that the matter be investigated thoroughly.
He said: "There will always be some people who break the law, the vast majority of soldiers know the law and they also know what the right thing to do is."
Last week former armed forces minister Adam Ingram admitted misleading MPs over British troops' hooding of Iraqi prisoners. He had said that hooding was only used for security reasons rather than interrogation purposes.
The inquiry has previously heard that both Mr Hoon and Mr Ingram were copied in on memos stating that Mr Mousa had been hooded.
The public inquiry was set up after the court martial found no-one guilty over the death.
It has so far heard from more than 230 witnesses, including soldiers, a former minister and several Iraqis detained with Mr Mousa who were also subjected to hooding and forced into stress positions.
These techniques were banned by the Geneva Conventions and by a government ruling in 1972, following an investigation into interrogation in Northern Ireland.
The inquiry wants to know who in authority sanctioned, condoned or ought to have known of their use in Iraq.