Ministers are routinely providing legal cover for the intelligence services where there is a possibility of information being extracted through torture abroad, under a so-called “James Bond clause”, a human rights group has alleged.

Reprieve is planning to launch a judicial review of the practice of repeatedly granting protection – in effect immunity from prosecution – for MI6 or GCHQ officers in cases involving detainees held overseas.

The legal challenge follows a report by parliament’s intelligence and security committee (ISC) earlier this summer on rendition and mistreatment of terrorist suspects since 9/11.

The claim will add to pressure on the government to hold a judge-led inquiry into the UK’s involvement in human rights abuses. The Council of Europe’s new commissioner for human rights, Dunja Mijatović, has sent a letter to the prime minister saying it would send out “a positive signal to other … states” which still have to “provide a full account of their involvement in rendition and secret detention programmes”.

Reprieve, which campaigns against rendition, claims that a pattern of authorisations by ministers under section 7 of the Intelligence Services Act 1994 – highlighted in the ISC report – is unlawful because it breaches the European convention on human rights and other treaties to which the UK is a signatory.

Section 7 is sometimes known as the “James Bond clause” because it provides a legal amnesty for spies to commit abroad what would otherwise be crimes.

The report of the ISC, which is chaired by the former attorney general Dominic Grieve, said: “We have found that, when SIS [MI6] or GCHQ refer a consolidated guidance case [about detainees abroad] to ministers, they routinely seek, in parallel, an authorisation under section 7 of the Intelligence Services Act 1994, which can provide protection for their officers from domestic civil and criminal liability.”

The full title of the guidance is: Consolidated Guidance to Intelligence Officers and Service Personnel on the Detention and Interviewing of Detainees Overseas, and on the Passing and Receipt of Intelligence Relating to Detainees.

An MI6 official told the ISC: “We are … always going to go for a section 7 authorisation. Because, you know, why should my officers carry the risks on behalf of the government personally?… So we will go for belt and braces on this.”

The official denied that “section 7 authorises [MI6] to carry out CIDT [cruel inhuman or degrading treatment] and torture”.

The ISC report called for greater transparency surrounding the use of section 7 authorisations and said their “scope and purpose should be addressed in the consolidated guidance”.

Reprieve alleges that the section 7 authorisations are “the modern equivalent of the torture warrants [for interrogation] issued by the privy council” in the 16th and 17th centuries.

In its letter before action to the foreign secretary, Jeremy Hunt, Reprieve says: “There can be no licence for torture or for any other inhuman or degrading treatment.

“The ISC report indicates that ministers believe they have the power to grant authorisations under section 7 in circumstances where there is a serious risk of torture and the defendants regularly seek and are granted such authorisations where there is a real risk of CIDT (indeed it also appears that such authorisations are granted where CIDT is known to occur).”

The letter also draws attention to evidence given to the ISC by senior ministers, including Theresa May, Boris Johnson, Philip Hammond and Amber Rudd, about how absolute a ban on torture they believed the consolidated guidance constituted.

The ISC concluded that the ministers’ “contrasting views clearly illustrate the dangerous ambiguities in the guidance”. The letter before action notes: “It is clear from the report that a number of ministers believed they could grant an authorisation under section 7 where there was a serious risk of torture.”

Maya Foa, director of Reprieve, said: “In recent months the prime minister has had to apologise for the UK government’s role in the ‘appalling’ kidnap and rendition of a pregnant woman and her husband [Fatima Boudchar and Abdel Hakim Belhaj], U-turn on an attempt to hold a ‘light-touch’ review of the torture policy, [and] face a damning report that revealed hundreds of cases of British complicity in mistreatment. The public now need urgent reassurance that ministers cannot legally authorise involvement in torture or mistreatment in any circumstances.”

Rosa Curling, at the law firm Leigh Day which is representing Reprieve, said: “The foreign secretary, the Secret Intelligence Service and GCHQ seem to think they can authorise conduct even if there is a serious risk of torture and/or cruel, inhumane or degrading treatment. These section 7 authorisations are being used like modern-day torture warrants. Our client considers this to be immoral and unlawful.

“Our client has written to the government seeking confirmation that the secretary of state will refuse to authorise any conduct where he knows or believes torture and/or cruel, inhumane or degrading treatment will or may take place or there is a serious risk of it.”

A government spokeswoman said: “The security and intelligence agencies are subject to a strict legal framework and robust independent oversight, including by the intelligence and security committee of parliament, the investigatory powers commissioner and the investigatory powers tribunal. All of their work must be necessary, proportionate and in accordance with the law.

“The government is carefully considering the intelligence and security committee’s reports into detainee mistreatment and rendition issues and will respond formally in due course. Consideration will also be given to the separate calls for another judge-led inquiry.”

Sir Adrian Fulford, the investigatory powers commissioner, is examining the consolidated guidance in the light of the ISC report.