Access to the secret report has become central to securing Senator Lambie's crucial vote to restore the ABCC, and she voted against the bill, which was defeated by one vote, last week. When he released his 1800-page interim report in December last year, Mr Heydon said the 87-page third volume needed to remain secret to "protect the physical well-being of those witnesses [appearing at the commission] and their families. This is unfortunate, because the confidential volume reveals grave threats to the power and authority of the Australian state". In his letter to Senator Lambie, Mr Abbott said there was ample publicly available evidence supporting the need to restore the ABCC, the Howard-era watchdog dismantled by Labor in government, and gave an insight into the contents of the third volume. "I can advise that the confidential volume reports on threats of violence, and an act of violence, against witnesses called or likely to be called to give evidence before the Royal Commission," Mr Abbott wrote. "I invite you to contact my office to arrange for a confidential briefing by a senior officer in my department on the confidential volume. This will be an oral briefing summarising the report that does not contravene the non-publication direction."

Mr Abbott goes on to "assure" Senator Lambie that the secret report "does not contain any reference to political corruption or any matter that would harm the reputation of the Liberal Party". In her response later on August 12, Senator Lambie, who has been asking for months to read the confidential volume, wrote to Mr Abbott and said the report should be made available to senators, with appropriate safeguards, to inform her vote on the ABCC bill. She also asked for the construction union, the CFMEU, to be deregistered and for a separate confidential report written for the then Victorian Napthine government by the current head of the construction watchdog, Nigel Hadgkiss, to be released in exchange for her vote. "If the government could comply with these conditions, I would happily co-operate to ensure the above legislation passes the Senate."

On Tuesday evening, Labor workplace spokesman Brendan O'Connor said the offer of a briefing was "concrete evidence" of the commission's political objective and that "he's using this secret report as political leverage". A spokesman for the Prime Minister emphatically denied the offer of a briefing was a "bargaining chip". The spokesman said Senator Lambie had sought access to the secret document and the proposed briefing would provide information about the report but not its detail, "ensuring the briefing would be entirely consistent with the non-publication order made by the commission". "No other crossbencher has asked for a briefing at this stage. Any request would be considered. There is nothing 'transactional' about the proposed briefing," the spokesman said. Senator Lambie has also corresponded with Mr Heydon in recent months about the report, with the commissioner stating in a May 14 letter the "extent to which the confidential report should be disseminated is primarily a matter for the Prime Minister, Commonwealth Ministers of the crown and the State Premiers."

"I fear that any significant dissemination of it would result in a destruction of confidence and create the possibility of danger to physical wellbeing of witnesses and their families." In a response on May 21 to Mr Heydon, Senator Lambie argued "the government in the past allowed senators to view top secret reports such as the DLA Piper Vol 2 which contains explosive allegations of defence abuse". "I humbly ask you to reconsider your decision and my request." Mr Heydon, who is under pressure to quit over his acceptance of an invitation to speak at a Liberal Party fundraiser, has delayed again revealing his decision on his own fate as commissioner. Liberal Democrat David Leyonhjelm said: "Crossbenchers blackmail the government. That's how we do business."