An SAS trooper’s secret evidence criticising the military’s torture resistance program has been mistakenly distributed to civilian organisations and the defence department.

The evidence, given to a Senate inquiry, disclosed the identity of a senior intelligence official and revealed controversial training methods.

In March, SAS trooper Evan Donaldson gave “in camera” evidence to the inquiry examining the military’s use of resistance to interrogation (RTI) training.

The defence force uses the training to prepare soldiers for possible capture, but Donaldson – who was also suing the defence department – was highly critical of its use, saying he was subjected to degrading and harmful practices in 2006 that caused him lasting psychological damage.

Donaldson said trainees were effectively used as guinea pigs for intelligence officers to practice interrogation, and alleged he was exposed to 96 hours of physical and mental stressors, including a serious and humiliating assault.

Donaldson named a senior Australian intelligence officer who led his interrogation. He also described colleagues who shared his concerns about the RTI program, and spoke in detail about the training methodology.

Last month a transcript of his evidence was mistakenly sent to every witness that appeared before the inquiry. That included the Department of Defence, which Donaldson had strongly criticised, and civilian organisations such as the Australian Psychological Society.

It was also sent to a Parkes GP, Steven Scally, a veteran who went through the RTI program.

Scally confirmed to Guardian Australia that he had received the transcript of Donaldson’s evidence. He said he had assumed the contents were approved for release, but was soon contacted by the Senate, and told to return the evidence.

Scally said he had shredded the document.

Donaldson is now considering legal action, saying his privacy has been breached and he has suffered repercussions.

“We’ve engaged lawyers for advice as to what to do. But they can’t take it back,” Donaldson told Guardian Australia. “I don’t know if there’s been copies made. One of the things that concerns me is that I gave evidence about intelligence officers.”

Donaldson realised what had happened when he was sent the transcript via email.

“When I received the transcripts of the evidence, I was too sick to read them, it’s something that triggers my health condition, but my wife looked at them,” he said. “I can see how, and I can hope, that this is just a mistake, but it’s a pretty big mistake.

The mistake was made in the secretariat for the Senate standing committee for foreign affairs, defence and trade, which has since apologised and asked for witnesses to send the transcripts back.

A secretariat spokesman said changes to its processes had been made to ensure the error was not repeated.

“The bottom line for this is that it was a handling error, an administrative error within the secretariat. It was something that was drawn to the secretariat’s attention when it was made,” the spokesman said.

“It’s very regrettable … but the committee is obviously aware of it, and now we’re dealing with it with the individual concerned,” he said.

Senate committees can take evidence that is not open to public viewing.

A committee can elect to publish material in its report, but the disclosure of evidence taken in camera without the formal authorisation of the committee could be considered a contempt of parliament.

The secretariat’s spokesman said he was confident the inadvertent release did not constitute contempt of parliament.

Alleged disclosures of in-camera evidence have in the past been referred to the privileges committee to determine the nature of the breach and what actions should be taken. The secretariat would not say whether that had occurred.

The committee’s chair, Labor’s Alex Gallacher, wrote to Donaldson to apologise last month, saying the mistake was the “result of an administrative error by the secretariat”.

“On behalf of the committee I take this opportunity to again apologise for any harm this inadvertent release of evidence may have caused,” Gallacher wrote.

“Your email makes a serious allegation of intimidation by the chief of army and his staff after your appearance at the hearing … The committee is very concerned by these allegations,” he said.

The department of defence referred all questions on the issue to the Senate, including queries on what it had done with the transcript of Donaldson’s evidence, and whether it was concerned about the dissemination of training methodology.

A spokesperson said the allegation that Donaldson had been intimidated was untrue.

Donaldson has made a number of complaints about his treatment by defence in recent years, including the changing of his rank and the refusal to allow him on a deployment to Afghanistan. He sued the defence department and settled the case this year. Donaldson is also suing the SAS Association for defamation, alleging it wrongly claimed to its members that he was not an SAS member.

