British soldiers have “lost their capability” to interrogate terrorist insurgents because of strict new rules on questioning that even ban shouting in captives’ ears, military chiefs have warned.

The rules — detailed in court papers obtained by The Telegraph — also prevent military intelligence officers from banging their fists on tables or walls, or using “insulting words” when interrogating a suspect.

The regulations replaced a previous policy that had to be withdrawn after a series of legal challenges and the death in custody of Baha Mousa, an Iraqi detainee in Basra.

But there is growing disquiet within the ranks that the latest guidelines, officially called Challenge Direct, are so stringent that it makes interrogation pointless.

There is also concern that the rules can be so easily breached — especially given the pressure under which soldiers are operating — that military personnel will be left exposed to legal claims and possible disciplinary action.

There was global condemnation last week when a Senate report in the United States disclosed how the CIA had systematically tortured detainees in the wake of the September 11 attacks. Despite this, British military chiefs fear the current restrictions on Army interrogators are hindering the gathering of information. They insist interrogations can be vital in thwarting future terrorist attacks and in combating insurgents in hostile environments.

Col Tim Collins, who made a celebrated eve-of-battle speech during the Iraq war and now runs a private security company with expertise in intelligence gathering, said: “Since I was serving, the rules on interrogations have been tightened up because of the lawyers. We [the military] are no longer able to carry out tactical questioning.

“The effect of the ambulance-chasing lawyers and the play-it-safe judges is that we have got to the point where we have lost our operational capability to do tactical questioning. That in itself brings risks to the lives of the people we deploy.

“These insurgents are not nice people. These are criminals. They behead people; they keep sex slaves. They are not normal people.”

Lord West, the former First Sea Lord and national security adviser, said: “We have gone too far in letting people take us to court.

“While these insurgents are chopping people’s heads off and raping women, the idea they can take us to court because somebody shouted at them is ridiculous.”

In an interview with The Telegraph, Michael Fallon, the Defence Secretary, voices his concern about the legal scrutiny on British troops. He says he is gravely concerned about the rising cost of legal cases “that turn out to be completely spurious”. He added: “What’s important for us is to understand the legal scrutiny that we are under all the time now, the cases that are being brought sometimes spuriously by law firms representing people who claim they were wrongly detained.

“Our Armed Forces are under a huge degree of scrutiny.” He said he feared this could inhibit commanders in the field in future.

The rules on interrogation are contained in a Court of Appeal judgment handed down in the summer and obtained by The Sunday Telegraph. The policy was introduced two years ago after outrage over the death of Mr Mousa, an innocent Iraqi civilian who was beaten to death while in British custody in Basra in 2003. An inquiry into his death, published in 2011, disclosed that he had been subjected to sustained and gratuitous beatings by soldiers from 1st Battalion the Queen’s Lancashire Regiment.

The legality of the Challenge Direct interrogation technique was disputed by lawyers acting for Haidar Ali Hussein, an Iraqi civilian arrested in 2004 who alleged that during his detention he had been subjected “to substantial periods of shouting”. Mr Hussein was also claiming damages from the Ministry of Defence over alleged mistreatment.

Although Mr Hussein’s detention predated the new policy, his legal team had argued that Challenge Direct should be ruled unlawful because it constitutes “inhumane treatment” in contravention of the Geneva Convention.

The Court of Appeal threw out Mr Hussein’s challenge to the interrogation policy — but in doing so disclosed how the technique works and when it can be applied. It also highlighted a series of breaches.

The judgment handed down by Lord Justice Lloyd Jones, the Lord Justice of Appeal and one of the most senior judges in the country, discloses what appear to be enormous constraints under which interrogators must now operate.

One source said: “This ruling shows just what a nightmare it now is for interrogation teams. Interrogators have been left wondering if it’s worth the bother.”

The previous policy — known as “Harsh” — gave soldiers the right to “shout as loud as possible [with] uncontrolled fury” at a captive. It also permitted soldiers to show “psychotic tendencies”, and aim “personal abuse” at a captive who could be “taunted and goaded”.

The Challenge Direct technique reined in those excesses and allows shouting for only a few seconds at a time — the actual length is redacted for security reasons in the ruling — under strict regulation which is designed only to gain a captive’s attention.

The judgment discloses that under the new policy interrogation “must not be insulting” and that a “captured person’s attributes must not be ridiculed”. The policy adds that “the questioner must not touch the captured person” and “must not shout into the subject’s ear”.

The Challenge Direct approach can only be carried out with prior permission and if the session is being recorded to prevent abuses. “There must be no intimidation of any kind,” state the rules.

Lord Justice Lloyd Jones and two fellow Court of Appeal judges ruled the Challenge Direct policy lawful in itself, but on reviewing many hours of video evidence decided that on a series of occasions, interrogators had breached it. The judges were shown recordings of the interrogations of 13 captives in Afghanistan who were subjected to the Challenge Direct technique. They found a number of occasions when the rules had been broken.

Such breaches, the senior judges found, included an interrogator who “held the hand of the captured person during the use of Challenge Direct, a breach of the prohibition on physical contact”; an interrogator who “slammed the desk with his hand” and one who “slammed the wall with his hand”.

Judges also found other violations, including a soldier who used “insulting words throughout an interview” and “vulgar abuse” at a captive. They said the “most striking example” of a breach of the policy was when an interrogator “suddenly moved forward from a crouching position so that his face was right in front of the captured person’s. This was physically intimidating.”

But the judges said the breaches did not in themselves make the technique unlawful. “I have come to the clear conclusion that the policy which the appellant seeks to challenge does not involve any violation of the duty of humane treatment or any other relevant standard under the Geneva Convention,” said Lord Justice Lloyd Jones.

The judge questioned why Mr Hussein had been allowed to bring the case, given that he was never subjected to the technique. Mr Hussein was represented by Public Interest lawyers, a human rights legal firm which has brought a number of successful claims against the British military. The firm is led by Phil Shiner, who represented Mr Mousa’s family.

Mr Mousa, 26, a hotel receptionist and a father of two children, had been held in custody for 36 hours, for the majority of the time hooded, and suffered at least 93 injuries prior to his death. Practices such as hooding had already been banned by the Army, while the case highlighted the lack of control exercised by senior commanders on the soldiers conducting his interrogation.

The MoD has paid out millions of pounds in compensation and costs to hundreds of Iraqis who complained that they were illegally detained and tortured by British forces. The payouts followed legal rulings that abuse cases can be brought in Britain.