The senior lawyer appointed by the Prime Minister to investigate the GCSB wrote a report which was more detailed and highly classified than the one released.
The existence of the highly classified version of the report was revealed by Air Marshal Sir Bruce Ferguson, who was a former director of the GCSB and consulted on a draft of the report. He said the report released was "a sanitised version".
"The draft I read wasn't just sensitive. It was more than that."
Green Party co-leader Russel Norman expressed surprise over the existence of a more highly classified version of the report. "If it's true they sanitised the report before releasing it, it means there's another version somewhere. It means they have not been completely straight with us."
Sir Bruce said he had been asked to read the first draft of the report before being interviewed by its author, Rebecca Kitteridge, the Cabinet secretary seconded by John Key to carry out the inquiry.
He said he read the report at the GCSB where his cellphone was removed before entering the building.
"I sat in [a] room with a guard closely monitoring, making sure I didn't take photographs, didn't take notes."
He was not shown any appendices, which were never released because of their security classification, and sections of the draft were obscured so he could not read them. He said he read the version released publicly and "there was lots missing".
A spokesman for the GCSB said the production of the final report saw it prepared for public release with classified information moved into the appendices. A spokeswoman for the Prime Minister said the only copy Mr Key ever received was released in full with classified appendices withheld.