© Photograph: ReutersA British soldier guards Iraqi prisoners in the city of Basra in April 2003.
In the Lebanese capital of Beirut, far from the theatre of war in Iraq and his office in Birmingham, one of Britain's leading civil rights lawyers has gathered some of the most damning allegations ever levelled against this country's armed forces - certainly since the worst days of Northern Ireland's Troubles.

As Britain's invasion of Iraq approaches its 10th anniversary in March, Phil Shiner - who founded the Public Interest Lawyers group - and members of his team have held face-to-face meetings with survivors of alleged abuse and torture by British soldiers and intelligence officers and with relatives of those unlawfully killed during and after the war that defined the premiership of Tony Blair.

The statements - 180 of them, with 871 to follow - go before a judicial review hearing at the high court in London next week in a claim seeking to demonstrate that Britain broke international laws of war by pursuing a policy of systematic torture.

The testimony is shocking, such as from "Khalid", a detained Iraqi civilian: "[A British soldier] then grabbed my penis and dragged me around the floor while holding it. He also made me squat up and down whilst naked and inserted his finger into my anus. I would have preferred to have been killed than subjected to this."

A prisoner called Halim claims he was told: "Fuck you and fuck Islam!" by a soldier who then "opened the belt of my trousers and said 'now jiggy jiggy'. The soldier put his boot in my chest and pulled my trousers down ... The soldier put his foot on my chest ... lifted me in the air and turned me on to my front ... He started rubbing his penis on my back while the other soldiers watched. I felt him ejaculate on my back ... I was so upset but he spat in my face. He kicked me and started slapping me."

A man called "Asif" claims that when soldiers came to arrest his elderly father, he said: "So you are the British people?" He testifies that the soldiers paralysed the old man with the blow of a rifle butt and stamped on Asif's young son's head when the boy tried to help his grandfather. "What I know of the British people is the opposite of what you are doing," said Asif.

And so it goes on, witness after witness, in papers and videos before the court on 29 January, calling for a public inquiry into what is presented as an orgy of sadism, outlawed interrogation methods and unlawful killings by soldiers and intelligence officers against Iraqi civilians and prisoners of war between 2003 and 2008. Iraqi soldiers who surrendered - supposedly protected by the Geneva Conventions - allege that they were forced to sit for hours in harsh sun, kicked, beaten and photographed going to the toilet.

Civilians say they were subjected to hooding, beating, threats of rape and execution, forced nakedness and maintaining stress positions, violence against wives and children, ritual humiliation. And they claim that others, like Baha Mousa, were beaten to death. They say walls of noise were used to drive the prisoners mad and cover the sounds of abuse and pain.

The British government will argue in court that this apparent litany of abuse by troops it sent to "liberate" the Iraqis does not warrant a public inquiry, since it was not "systemic".

But the high court will be asked to rule that this position is untenable given the weight and range of the allegations. Shiner and lawyers for the families of those killed and survivors of the abuse say the inquiry is a fundamental requirement of articles 2 and 3 of the European Convention on Human Rights, on the right to life and prohibition of torture.

According to Shiner and his supporters, the decision of the high court will signal whether, 10 years after the invasion, Britain is prepared to reckon with its own legacy in Iraq.

"This is the crucial moment of decision," says Professor Andrew Williams, author of a book on the most infamous single case to date, the torture to death in custody of an innocent hotel receptionist, Baha Mousa. "This is our last chance to get to the truth and find out what went on. It's the last chance to see who is responsible."

The legal issue at stake is whether the other abuses were isolated incidents of which commanders were unaware, as the government insists, or systemic and authorised as policy. With these cases comes the contention that the violations were systemic and thereby illegal - with responsibility reaching senior command level - which would put the state in breach of international law and necessitate an independent public inquiry. The victims' claim before the court says: "No Iraqi appeared to be exempt from ill-treatment from arrest onwards."

The MoD says the Baha Mousa inquiry, which investigated the killing of Mr Mousa and torture of several other civilians, dealt with any general problems of detention and interrogation. That inquiry reported last year and condemned the use of hooding and stress positions, supposedly outlawed by the UK government in the 1970s.

The MoD also points to its own Iraq Historic Allegations Team, established in 2010, which it says is a sufficient response to the allegations. The team was made up of Royal Military Police officers appointed to internally investigate unlawful killing and torture. But the appeal court ruled in November 2011 that the RMP had been "substantially compromised", its members having been involved in the system of detention itself.

Williams's book, A Very British Killing: the Death of Baha Mousa, details the killing and flawed investigation and prosecutions which followed, and exposes what he calls "a culture of callous indifference that infected a whole battalion and permeated far up the command chain, both military and governmental. What happened to Baha Mousa, and how the army and the government responded to his death, is emblematic of a whole system in operation."

Moreover, says Williams, who teaches law at the University of Warwick: "The international principle in criminal law is that you look at the connection between commanders and what happens on the ground. Responsibility is supposed to rest with those at the top. It's no excuse for ministers and officials to say they didn't know what was happening.

"These are international obligations. This is what we demand of others, but we do not demand it of ourselves. What kind of message does that give to the world about who we are?"

Shiner's case is built in part on the conviction of the UK at the European court in Strasbourg in 1977 of "inhuman and degrading treatment" of detainees in a case brought by the Irish Republic.

Trial lawyers, led by Michael Fordham QC, will argue that while the Baha Mousa inquiry "may have shone a torch into a dark corner", what is now before the court is more like "a stadium in which we will switch on the floodlights".

Shiner's files are disturbing: page after page, case after case offers detailed gruesome particulars. The worst abuses took place in facilities named by the British as Battlecamp Main, Camp Stephen, Camp Bucca and Camp Breadbasket; also at Shaibah logistics base, a contingency operations base, and holding facilities including one soldiers called "the guest house". But many also occur in people's homes and at street demonstrations.

Shiner argues that five illegal "state practices" are established by the evidence, which includes videotaped interrogations. "We've got the training materials, we've got the policy documents," says Shiner. "Violence was endemic to the state practices and part of the state practices."

One "state practice" is "the use of trained coercive interrogation techniques, as a matter of policy ... They knew full well that what was happening was unlawful, right to the top," says Shiner. "It was all being trained at a facility in Britain called Chicksands" - an army intelligence base 50 miles north of London in Bedfordshire.

His argument is borne out in a history of British torture by Guardian journalist Ian Cobain - Cruel Britannia - which tracks permissions required to enact specific techniques of abuse up to ministerial level. Cobain also reveals an interrogators' Powerpoint tutorial called "Any Questions" which trains in the use of forced nakedness and sensory deprivation, including such instructions as: "pull back foreskin, spread buttocks".

The second "state practice", claims Shiner, is "an unlawful detention and internment regime which did not meet international obligations", with regard to tribunals, combatant status for PoWs and obligations to civilian suspects during arrest and detention.

Third was a "rolling programme of strike operations" to apprehend civilians - "blowing doors off so that 20 soldiers can run into houses at one or two in the morning while women and children are sleeping, men dragged from bed and rifle-butted - one man was simply shot in bed - women and children abused".

There is also unlawful use of lethal force - using illegal rules of engagement after the wartime phase has ended. "The rules change during an occupation, but the practices did not, and a lot of people were killed. The judges are going to hear about a grandmother who was abused and a few hours later found in a body bag," Shiner says.

"What we're dealing with are the widespread abuses," he says. "We say to the ministry and government: 'Don't say you didn't know - what you can do is explain why you failed to do anything about it'."

Sexual depravity is a recurrent theme. Apart from routine sexual assaults, prisoners' faces are superimposed on to pornographic videos in order to blackmail them; female interrogators strip and feign seduction of prisoners in return for "information".

Abuse of Islam is another regular feature. One prisoner says he "could not believe" what he was seeing when a British soldier pretended to defecate on the Qur'an. "It's all carefully thought through," says Shiner. "It's as though the army took a manual on Muslim culture and reverse-engineered it. Things were done that are calculated to make them go mental."

In his own arguments to court, Shiner says: "All of these allegations involve circumstances in which it can be said that the UK state knew, or ought to have known" about breaches of international law. "Its response, or lack of one, is highly pertinent," says the claim.

"Military facilities at which abuse occurred were under the command of the relevant commanding officer" and "each detainee was medically examined at various points by doctors ... It is inconceivable that senior officers did not witness what was happening, or otherwise be aware of these incidents and practices."

Case studies

Radhi Nama was a teacher in his early 50s who was taken into detention at a unit holding facility.

He was hooded, his hands tied behind his back, and - as witnessed by his son - pushed by a soldier so that he "fell forward" and was thrown into a vehicle. During the subsequent interrogation, Nama's son said that his father had been "made to squat on the floor with his hands on his head".

Radhi Nama died on 8 May 2003 and was said, following a Royal Military Police investigation, to have died of "natural causes" involving a heart attack. There was no postmortem examination carried out, nor was a death certificate issued.

Kh M was one of the first two serving Iraqi soldiers to surrender to the British as prisoners of war, thereby placing themselves under stringent laws of war that protect PoWs.

He testifies: "A very muscular soldier ... hooded both of us. We were left to kneel in the sun for hours. If I moved position or bent my head forward at all, a soldier would come and kick me hard - shouting 'shut up!' and 'fuck you'. I was kicked many times.

"During this time, one of the soldiers kicked me hard in the mouth, which caused three of my teeth to fall out later that day ... I could see through the hoods a soldier taking photographs of me when I went to the toilet."

"Large military dogs" were also used to terrorise him during his time held in captivity.

JST was placed under arrest while at home

"The soldiers started throwing me to each other as though I were a doll ... As each soldier caught me they would punch me ... I could hear the soldiers laughing ... I was thrown to the ground ... I felt a soldier's boot on my head pushing my head to the ground.

"[In detention] a soldier started hitting me and pinching me on the buttocks ... He then grabbed my penis and dragged me around the room while holding it ... He also made me squat up and down while naked and inserted his finger into my anus ... This was a serious affront to my religion."

Baha Mousa

Baha Mousa was one of 10 Iraqis detained in Basra in September 2003 by members of the 1st Battalion The Queen Lancashire Regiment on suspicion of being an insurgent.

The 26-year-old died two days after his arrest and a post-mortem examination found he had suffered asphyxiation and at least 93 injuries to his body, including fractured ribs and a broken nose.

Seven British soldiers from the Queen's Lancashire Regiment were charged in connection with Mousa's death and abuse of Iraqi prisoners and a court of appeal ordered an independent inquiry.

Corporal Donald Payne was jailed for a year and dismissed from the army after pleading guilty to inhumane treatment of Mousa. The six others either had the charges dropped or were acquitted.

Defence Secretary Des Browne announced a public inquiry into Mousa's death and the Ministry of Defence agreed to pay £2.83m compensation to mistreated detainees.

The inquiry concluded that Mousa's death was the result of a combination of his weakened physical state - caused by factors including lack of food and water, heat, exhaustion, fear, previous injuries and the hooding and stress positions used by British troops - and a final struggle with his guards.

The report also concluded that British soldiers had inflicted "violent and cowardly" assaults on Iraqi civilians, subjecting them to "gratuitous" kickings and beatings and included 73 recommendations to prevent a repeat of the failings.