Edited versions of secret documents relating to the conditions under which lawyers’ or journalists’ phones and emails can be intercepted are to be released by the government in a case brought against the intelligence services by two Libyan victims of rendition.

The government’s previously trenchant refusal to reveal the policy papers has been a key issue in a claim brought on behalf of Abdel Hakim Belhaj and Sami al-Saadi who, along with members of their families, were kidnapped and sent to face punishment in Libya in 2004.

The change of position came on Wednesday shortly before a rare public hearing of the investigatory powers tribunal (IPT), which examines complaints against the intelligence services and government use of surveillance. Government lawyers refused to either confirm or deny whether legally privileged material obtained through surveillance has been misused.

However, while a substantial number of documents were said to be due for release on Thursday following a review, lawyers for Belhaj and al-Saadi were heavily critical of their format. Rather than providing copies of records that would also show the extent of redactions made on national security grounds, the authorities are expected to provide retyped documents containing the text which can be released.

Dinah Rose QC, acting for the Belhaj and the al-Saadi families, told the tribunal that the edited way the documents were being released was not acceptable.

“That means that there will be less information than there would be in redacted documents, not least that we are not going to be able to see the extent of the redactions.”

The case before the IPT alleges that the intelligence agencies or government spied on the men’s communications with their lawyers, damaging their right to a fair trial in their claim for compensation for kidnap and torture.

The Belhaj and al-Saadi families claim they were kidnapped and “rendered” to Libya in a joint MI6-CIA operation in 2004. The IPT is currently hearing a complaint brought by the Belhaj and al-Saadi families, who are supported by legal charity Reprieve and represented by law firm Leigh Day.

James Eadie, counsel for the government, GCHQ, MI5 and MI6, said there would be disclosure of “edited documents” which indicate the exact words used. “Where it is necessary to edit for national security reasons, that will be clear.”

The disclosure of the documents was agreed following negotiations between the authorities’ legal team and legal counsel for the tribunal, who will receive them on Thursday.

The director of Reprieve, Cori Crider, said: “This evidence is welcome but long overdue. It’s plain the government hopes to avoid the central question in this case: has private lawyer-client material improperly made its way into the hands of officials or lawyers involved in the torture claim? Time will tell, and we will just have to see what emerges from the documents tomorrow to find out whether the policies are worth the paper they are printed on.”

The complaint quotes as evidence accounts published in the Guardian about the Tempora system based on documents revealed by the US National Security Agency whistleblower Edward Snowden as part of his attempt to expose what he has called “the largest programme of suspicionless surveillance in human history”.

“Legal professional privilege”, as it is formally known, allows legal advice between clients and their lawyers to be kept private. According to the Law Society, which represents solicitors in England and Wales, it ensures that “certain documents and information provided to lawyers cannot be disclosed at all. It recognises the client’s fundamental human right to be candid with his legal adviser, without fear of later disclosure to his prejudice. It is an absolute right and cannot be overridden by any other interest.”