Grave allegations of torture and inhuman and degrading treatment by British soldiers and interrogators in Iraq "cry out" for an immediate public inquiry, Court of Appeal judges have heard.
Michael Fordham QC, representing a group of Iraqi civilians who claim they were mistreated, told the court: "There are sometimes matters of such grave concern as to cry out for an independent inquiry."
That was the case "whether it is the role of the intelligence services in relation to the treatment by foreign states of people who are in their custody or whether, more recently, it is the media, celebrities and the police", he said.
Mr Fordham told Lord Justice Maurice Kay, Lord Justice Sullivan and Lord Justice Pitchford that in relation to allegations of mistreatment in Iraq a public inquiry was "inevitable" and "must be commenced now".
More than 100 civilians are appealing against a December decision of the High Court which ruled against them in their bid for a public inquiry.
Two judges upheld Defence Secretary Liam Fox's refusal to order an immediate, wide-ranging investigation into whether there was systemic abuse, as opposed to ill treatment by "a few bad apples".
Lord Justice Richards and Mr Justice Silber ruled that due to other investigations already under way they were satisfied human rights laws did not require the defence secretary to order an immediate new inquiry.
Mr Fordham said at the start of an estimated three-day appeal: "The appellants seek a single public inquiry into the allegations that they were mistreated by British Forces in British-controlled detention facilities in Iraq between April 2003 and December 2008. There are credible allegations of cruel and inhumane practices across the whole range of relevant dates and relevant facilities."
Ali Zaki Mousa, from Basra, the lead claimant, alleges he endured months of beatings and other abuse in the custody of British soldiers in 2006-07. Mr Fordham said it was the appellants' case that "a public inquiry is necessary to discharge the Secretary of State for Defence's obligation to conduct an independent and effective investigation into their allegations of mistreatment" under human rights laws and that the "ongoing failure to discharge that obligation is unlawful".
The appeal is being contested by the defence secretary.